1.quite a few of these did have railways -of sorts- in the past. Whatever remains of it varies an awful lot. And if there are plans to revive these also.
2.quite a few smaller islands/nations are missing-as 181 already points at. As I just by coincidence was making lists of Caribbean and Pacific such states (to check other things, mostly if they would even have a bus-service) I noted that some of these are listed as having had a small tracks/railway-mostly for bringing exports to the nearest port. BTW-a fair nr of these states are in the GB-commonwealth and are listed on wiki as having Charles 3 as king.
3.several countries now only have railways for goods, not for passengers, like a brand new one in Abu Dhabi-UAEmirates.
4.I wonder myself what the minimum -in area, population etc is to sustain a railway. There is no rule that says that a country should have one.
The latest to have vanished from your list is likely the quite large but very thinly populated (former also communist) Laos-built by the Chinese as first step towards Bangkok/Thailand, with the Thai not being very fast in building their part-as hi-speed on normal gauge vs. the existing slow-speed on metergauge, though work on some sectors have now started.
And as also pointed out, Qatar does have a brand new, fully automatic and very cheap (single 50 cts, daypass 1,50-in € or $) 3-line metro network, complemented with a light rail and 2 different tramway systems- just used it a few weeks ago on a longer stopover.
And just by pure chance a mr. google led me to a site I did not know-a kind of competitor to the invaluable seat61: railwayhero.com. Offers very basic info on what runs in countries, seemed to be linked to the passes site of eu/interrail (heavily promoted and same format in the site).
It lists Eritrea as offering occasional touristy steam trains/excursions and more regular same for Colombia. I highly doubt if any tourist would be willing to visit Eritrea the last years, but thats beside this all.
And it seems one of these Caribbean commonwealth states- St.Kitts, is also listed as having a touristy excursion train, not daily. For me a definite first to see this. Well; nice this forum, will always bring some more unexpected news and info!