Very early in their history, it appears that the Uniswap team decided not to try to be the consumer-facing gateway to traders. Perhaps they were seeing the early versions of DEX aggregators and decided to keep their focus narrow—a very reasonable decision. From the v2 docs:
The third bullet-point above acknowledges the inevitability of trades being routed through Uniswap via aggregators.
The strategy for an aggregator like 1inch is: Figure out the algorithm that results in the user receiving the lowest price for a trade by optimally routing liquidity and minimizing gas fees.
The strategy for Uniswap becomes: Attract as much liquidity as possible so that aggregators have to route trades through their pools.
Is Uniswap making a wise decision by giving up the direct relationship with the trader? Only time will tell.