At the moment the miners for a block are awarded 12.5 BTC. Every 4 years this value will fall by half. For example, let's imagine that the prize value is 1.5 BTC for each block and that BTC's value against the dollar does not increase. In such a case, mining will not be very profitable.
At the same time, miners are also benefiting from the value of the fee. This time the fee values will increase. Then people will have to pay a high fee for bitcoin transfer. The biggest advantage of the Bitcoin system against banking systems was that they could shop without paying commissions to any brokerage house. If this happens, can bitcoin preference be reduced?
No really, only the BTC reward will be lowered but the BTC price will increase due to the law of supply and demand, less BTC less supply more demand, high prices.
You are assuming that bitcoin will be the primnary cryptocurrency and that there will always be demand. But it's possible that as fees rise, people switch to another cryptocurrency and bitcoin collapses.
Nothing is guaranteed in this space.