Everything comes at a cost, if you optimise for one thing you have to give up something else, monero transactions onchain might be private but like Bitcoin privacy tools you only have forward privacy if you bought on a KYC or dox'd yourself acquiring it so first you need to P2P which isn't as liquid as Bitcoin P2P so good luck getting in and out

Then you have operational risk, monera is constantly changing its hashing algo so ASICS don't get involved in their game or get involved for too long so you're constantly hard forking and ensuring your can never be sure the next hard fork won't introduce issues

You also take liquidity risk and if you don't know supply and issuance, it's not really something you'd want for long-term storage. The only use I could see for it is atomic swapping between monero and BTC as a hybrid coin-join but even that use case can be done in different ways