If we perpetually increase capacity ahead of demand, fees will never rise. Transactions will always be free or nearly free for users. This will not end well in a future where block subsidy ends and fees alone must support the security of the network (by incentivizing miners). If we did this, we are basically depending on mass adoption and skyrocketing price being guaranteed. That's probably not a good engineering decision.
Right now, transaction fee represents less than 2% of the miner's income. The remainder comes from the block reward. This percentage is going to increase in the future, but no by much. By 2030 or 2035, the tx fee may cross the 10% mark. If we increase the tx fee, that will do more harm than good. The usage will go down, and there will not be any significant increase in the miner's revenue.