Aside from comfort, or lack thereof, why not?
Comfort is a key concern, unapologetically.
Many face long commutes sometimes after a day of hard physical work and/or standing, and a seat, a comfy seat, is a very necessary thing.
Its also an aesthetic consideration and one about whether we convert transit here to being more like the U.S., where its seen as a service for the poor, for those with no other choice, rather than for a wide
range of people, including the broad middle class, who have a choice.
When you consider transit as an optional customer, your weighing cost, convenience, and comfort and your comparing it to driving for the most part.
Imagine Nissan trying to sell you an Altima featuring hard plastic seats. Right, not happening; because no one wants that, no one aspires to it, and it would be damaging to the brand to even consider it.
Transit needs to retain and woo more 'choice' riders. People who have a car at home and could drive.
You're not going to do that by making the service less comfortable and by making it seem like something a successful person wouldn't be caught dead using.