I should make it clear I've no present or past direct involvement with Crich, so none of what I say about them.
Agree with a lot of what's said, and it's not unique to transport preservation / museums. Volunteering in general has had a large contingent over the last 20+ years of people who were able to take (in some cases early) retirement on what was then considered a decent pension (which we're now encouraged to think of as 'gold plated / generous' pensions), whose home was fully paid for, and whose adult children were able to afford to buy a home without financial assistance.
There's a lot of angles to it.
How volunteering organisations treat new volunteers is very variable. Some volunteers go in with unrealistic expectations (we had a thread on here a year or two back where someone was offended because he wasn't out driving trains within months of joining a steam railway.) But many volunteer organisations have a very established core, and some make newcomers / young volunteers very unwelcome (and in some cases, the age at which someone is regarded as 'young' or the length of 'service' where someone is regarded as 'new' just keeps increasing.) There is a legitimate need for experience and training, but some organisations take the hierarchy and seniority thing a bit too far. On the other hand, I once ended up on the committee of a voluntary organisation within a month of joining.
Involving younger people is complicated - I was surprised to see that Crich (or their insurers and whatever the railway inspectorate's called now) allow 16 year olds as conductors. Most safety critical roles will have an age limit, and supervision of volunteers under 16 potentially brings organisations in to child protection territory. I'm aware some preserved railways have schemes for younger volunteers, but some will be reluctant to get in to that. Some people will regard this as un-necessary 'red tape' (although they may be the people who would be first with the pitchforks if anything happened to a member of their family) but it's an unfortunate fact that a few people seek out opportunities to work with children for all the wrong reasons.
Some organisations have too entrenched a 'department' structure with too much time and effort being put in to inter-departmental rivalry / disputes. Or where people who are willing and able to do some tasks being looked down on by others (can be the people who do the 'white collar' tasks looking down at those who are prepared to do the mucky jobs, but one organisation I've known had a treasurer who was very good at identifying and taking advantage of all the legitimate tax breaks for a charity, seeking out grants, and so on, but ended up being pushed out because they weren't often seen with their overalls on.)
The financial aspect is also not easy - if volunteering at (for example, a preserved railway) requires an individual to buy their own uniform and equipment, that's going to put some people off (although could be difficult if a volunteer was to get kitted out, then leave and not return their kit - an employer can offset that against the last week's wages.) Some volunteer organisations seem to expect volunteers to pay full public prices for tea and coffee and don't seem to want volunteers who can't afford it. On the other hand, I have volunteered for organisations where you can claim things like travel expenses. I'm not sure what the rules are round charities subsidising / paying for things like that.
I would echo the views expressed above and also the first line.
I've watched the video and would like to offer my own views.
A problem which seems prominent in the heritage sector....the lack of diversity and women participating... fully.
Another factor was the emphasis on outside influences e.g. Covid / cost of living / demographics as being reasons why volunteers are becoming difficult to recruit / retain. True, up to a point.
At no point however, probably because of a reluctance to admit to such, has another more relevant factor been mentioned...the one of internal culture.
In the 21st century, diversity is essential. It's futile to become / remain, reliant on a certain, male, demographic who want to play at trains. Equally, the adherence to the "this is the way B.R did things and so will we "...mantra. Those days / practices are, or should be, consigned to history along with their advocates.
I'm currently a volunteer with two organisations. Both are in stark contrast (not difficult) to my former railway.
DBS checks are mandatory....no problem there, they should be for all voluntary organisations.
I work with a range of occupations / ages / and both male / female volunteers. Three of the paid managers are female.
The roles are safety critical. Again, if you are familiar with, and have the mindset as a result, such environments, there's no problem.
As a normal, I'm expected to interact with normal's, having sense of humour helps!
I'm also expected to wear corporate attire. Fine, no different to work attire. Why the heritage rail sector is obsessed with archaic uniforms only they know. In many cases, it makes the wearer look ridiculous, even more so when a "big hat" is worn. I've seen plenty of station staff on heritage railways, stood around, looking ridiculous in hats that don't fit.
I'm also treated with courtesy.
Recruiting volunteers isn't that difficult. Retaining them is.
If the heritage sector is to remain active, it's no use trying to abrogate blame on external factors.
Take a deep introspective look at your cultures and, then, the difficult if not impossible for some, have the moral courage to change.
You may be surprised if you suddenly start to attract, and retain, a diverse range of volunteers as a result.