@node I don't know, maybe there are technical issues that prevent developers from working on it.
But more likely is that people just don't understand the value of such thing. Ethereum's MetaMask had existed for many years and other smart contract platforms quickly developed similar wallets. But bitcoiners only recently started to catch up with their Alby wallet. Monero is lagging behind because its community is much smaller
If no one creates a web wallet for Monero, I will probably start working on it myself soon