Why don't they hire a limo or coach then? Then they can have any seat they want, and drive whenever and wherever they want.
How dare a PUBLIC transport system have other members of the public on there that might end up sitting nearby.
When you reserve a seat, you can usually select your seat just like on a plane, so it's not as if the train operator just packs you in and makes you sit where you wouldn't choose. Why would you choose seats you didn't want, unless they were already booked - in which case you'd get another train if it bothered you so much.
Apologies people, I didn't express myself very well, I'll try to give an example of the point I wanted to make.
Many years ago I was on a fairly well loaded train, and on the opposite table to mine was a chap who had decided to pass his journey by studying some top-shelf magazines. It seemed possible he had deluded himself into thinking this would be a good way of initiating potentially exciting conversations with women. Nobody chose to sit at the table with him, so to extend his influence he started viewing his collection by holding them up in the air, allowing people behind him to see. Women would approach the vacant seats, hesitate, and move on. Eventually a couple of thick-skinned blokes sit down opposite him, and, somewhat disheartened, he desists.
Fast forward to today, and unaccountably, our hero still hasn't got a girlfriend. My 17 year old daughter is the lucky winner of the seat next to him in the seat reservation lottery. Even better, she specifically asked for a window seat, and now has to get past Mr Eligible to get to it. She is polite and well meaning in nature, and knows that if she moves to a now-rare unreserved seat, she is likely to deprive someone else of a seat. So she endures a journey next to an evidently lecherous oaf, or goes against the imprecations of the Toc to use the seat reserved for her.
My point is that in the days when seat reservations were a rarity, we all deployed many aspects of choice about where we sat, according to many criteria. Most people are fine to sit next to, even charming and polite, but some are evidently smelly, lecherous, drunk etc, and it really isn't some sort of elitist crime against the proletariat if we want to use public transport, but gently avoid the more anti-social minority.
Making seat reservation the norm on trains is just one of the ways that travel by rail has become less inviting, less pleasant, and more fraught than it needs to be.