People are certainly free to use alternatives, but if they aren't spinning up their own nodes what will they be using, another centralized node service? Most people aren't going to run their own node and for good reason, its expensive and profitless. Sure a cryptographic/economic layer on top of Ethereum could incentivize people to run nodes and have users pay for decentralization, but at the end of the day people will use Infura or a competitor because it is cheaper, and when these companies control who gets transactions they also influence who can make blocks.

Ethereum is fundamentally flawed in this sense - it only pays for mining (and in the future, staking). The work of routing and storing data is done by the most prolific miners and businesses reliant on Ethereum to keep it from collapsing; there is no sustainable model where a decentralized cohort of nodes can run Ethereum without fundamentally changing how Ethereum pays for infrastructure.