If travelling to Heathrow (during normal service patterns), it’s likely the first Piccadilly line train won’t be going to your destination and you’d need to either wait or change anyway. In this case there’s no hardship to breaking.
Aside from which, split journey anomalies (apart from self-created ones like journeys that cross a peak boundary) would be a bad precedent within TfL’s own network. It’s bad enough they’re there on services to Gatwick!
There is hardship - schlepping your bags up to the gateline to go out and back in.
But that doesn't matter. Anyone who wants to can use that workaround,
but most people will not. Thus an increase in income for TfL, and those who don't want to pay more having a workaround that suits them.
While this plan will abolish it, there are sneaky workarounds to pay less for TfL Rail now - a Super Off Peak Day Travelcard from Bletchley for both the outward and the return day is cheaper than other ticketing options. But I bet hardly anyone does that.
It doesn't matter if there are workarounds like this, because only a tiny number of people are going to use them. Just look at how many people pay extra for the Gatwick Express when you can pay less for an identical (and 1 minute quicker, if I recall) Southern service. And that doesn't even involve any faff at all!