If you want everything to confirm in the next block at tiny fees, then you need some other mechanism to pay miners once the subsidy is insufficient. That means either lifting the cap of 21 million and having constant inflation, or some other mining incentive like merged mining.
FWIW few pools already perform merge mining, but the income is extremely small since Bitcoin sidechain isn't popular.
All I heard was that the block size was not increased and this led to the creation of Bitcoin Cash. It was a fork but it is an altcoin (shit coin) while bitcoin remain the bitcoin.
But I am thinking recently that if the block size is increased, more transactions can be processed and the mempool will not be congested. If the block size can be in a way that 1 sat/vbyte transactions can all be processed in the next block, will this not be good?
If the block size is increased, what is its disadvantage to bitcoin network and miners?
I understand of people who have their interest in mining and related business and don't want transaction fees to be increased but I don't understand of those who are regular users and vote against it. I'll be frank and say that another problem is, what block size is the good size? Accepted by everyone? Some argue it's 4MB, some argue it's 1GB

Some ridiculous answers don't make any sense but it's still a good question.
That's good question, although there's no definitive answer. While i believe increasing block size should consider technological growth and cost to build and run full node, although it's hard to determine the lower limit. For example, should Raspberry Pi 5 (with SSD & 8GB) able to run full node?