Because there are many neophyte's who believe anything new is the "best ever". I have said for a long time ( and been attacked by the usual suspects) for daring to say that new trains have less comfortable seats than the trains they replaced.
Except not all of us do think that.
The Class 700 is cramped, but it is not really any worse than the Class 319 it replaced. (The ex-Thameslink 319s do have a bit of extra bonus legroom, but then I love how easy it is to move around a packed 700 which has been achieved by squashing the seats together a bit). The Electrostars on Thameslink were never anything other than temporary and should not really enter consideration.
The new Electrostars have more legroom than the originals, and not everyone wants tables, some prefer more privacy. The seats are set higher up which suits me better, being tall.
Though I must admit the Grammer E3000 is a better seat than the ironing board and doesn't give you appreciably less legroom at the same pitch. I have however never seen it anywhere other than a Desiro - is it a Siemens exclusive? It's a bit of a shame it was not chosen for the 700.
Meanwhile, if you do "deep" seats they soon end up with collapsed cushions like the awful Richmond seating found on Northern 153s and 156s. Now *that* is a bad seat.
And yes I've done long distance journeys in ironing boards, East Croydon to Bletchley and East Croydon to Bedford to name two.