Major cryptocurrencies like Bitcoin and Ethereum have foundations, but Monero does not. Why does one not exist? And will there ever be a Monero Foundation?
No "Monero Foundation" exists at this point because nobody has taken the initiative to create one.
The priorities and actions of both the Bitcoin Foundation and the Ethereum Foundation have been criticized by large parts of their respective communities. Sometime foundations can develop conflicts of interest with the community they were designed to support.
So far the Monero community has seemed more receptive to the idea of supporting projects with a more specific and well defined purpose via the Forum Funding System or "FFS". The closest we have seen to a "Monero Foundation" so far was the Monero Economy Workgroup or "MEW" and it was subsequently abandoned.
The Monero community seems very keen on not centralizing decisions more than necessary. In the short term, it more likely for more specific tasks to be funded by the FFS rather than a "Monero Foundation" being created with undefined or open ended objectives.
If any private party wants to create and fund a Monero Foundation on their own they are free to do so. The degree guarantee of community support (or lack thereof) would depend on its purpose and execution of its stated objectives.
"Foundations" in cryptocurrencies are a red flag IMO they always seem to popup after price surges in an attempt to create a PR arm off a decentralized movement, the Bitcoin Foundation was created in 2012 after BTC was already in mainstream and it did more damage than actually helped Bitcoin, not that it actually damaged the blockchain but the large public related the Foundation to Bitcoin itself and its mistakes over the entire BTC community. If I see some kind of Monero foundation surging I would run the other way.