Why are train tickets called "hard" seats?

Most train seats are hard seats, so most train tickets are named hard seats. This is also related to its price. Hard seats are relatively cheap, and hard seats in trains cannot be comfortable. I can only say that I tried my best not to feel uncomfortable. It was uncomfortable no matter how I sat. I didn’t sleep all night, and it was very troublesome to go to the toilet. You couldn’t get out even if the people next to the seat were asleep, and you were too embarrassed to disturb others. It can be said that it was It’s uncomfortable, so I try to drink as little water and eat as little as possible at night in order to prevent myself from going to the toilet