They are smart enough to know that if in history, Bitcoin total supply can be voted by Bitcoin nodes, community members to increase its total supply, there will be more events like this to increase Bitcoin total supply many more times. Then, belief in Bitcoin and its fixed total supply will be broken.
This idea is only from people who don't have bitcoin and hesitate to buy bitcoins. They want to have more bitcoins in total supply to have cheaper price to buy. They are for their benefits, not for benefit of the whole community. They also miss a point that if Bitcoin total supply can be increased, they will not get benefit in a long term too.
How is the 21 million Bitcoin cap defined and enforced?
Can Bitcoin's Hard Cap of 21 Million Be Changed?