Pre-covid I was on trains all around the country every day. The gradual and incremental improvements to timetables, stations, train sets and general state of the system is far, far better than the 1990s.
Timekeeping and capacity has got worse more recently because the system is bursting at capacity (and needs investment for sure) but to say it's stood still since the mid-90s is a nonsense. The main point of privatisation was to introduce private sector experience in growing a market, which has resulted in a billion more passenger journeys a year (750m-1750m in 25 years) - in a sense, it's been more successful than we can afford.
Show me a company which has made the kind of excess profits you describe and I'll show you plenty who lost fortunes on it - if anything the UK has learned that the state has to control the railways since it owns the risk, and might as well just get on with it.