For starters, Ethereum is not inflationary. ETH is minted and burned according to network activity. The more people making transactions (and paying for them) the less ETH will be created. It can even get to the point where some blocks lead to a net
burn of ETH.
Why would you stake? Even if the returns were low (compared to what?), people like me are interested in staking merely to help secure the chain at a (relatively low) cost compared to PoW chains, and having an efficient and secure blockchain opens up other opportunities for profit.
In my case, I am less interested in speculating with tokens and I am more interested in seeing a blockchain that can be an actual alternative for cross-border payments. I feel like by becoming a staker (and by working in projects that leverage layer-2 scaling networks [0]) I am contributing to that becoming a reality with a (relatively) low opportunity cost.
[0]: https://hub20.io