That's arguably how the scam most of their custom works. People have generally just come off a horrendous flight, half an hour waiting on the tarmac, bus gate, queues at immigration/passport control/customs/etc., are unfamiliar with the system and with the value of sterling, and will jump at all the signage mentioning the "fast train to London," not necessarily realising that (a) Paddington is pretty out-of-the-way for most places, and (b) £25 is appalling.
I say the sooner it's nationalised and abolished/absorbed into the Elizabeth line, the better.
Edit: One more thing to remember, it's free to use any train to transfer between the terminals (or rather it certainly used to be.) I don't know to what extent people tend to connect to a different flight at Heathrow though, I expect Schiphol has cornered that market.