Because no one will want to use different kinds of "moneys", if most people will save in bitcoin they will not want to swap it to other currency to make payments, and then swap some back to btc for savings. It is friction, also one would use monero, others zcash or whatever, it's troublesome. This is way they say best money takes all, it drives others out.
Discussion
If that was true Monero wouldn’t have 3 billion market cap..
It's not overnight, even btc it's not widely viewed as SOV, still XMR is loosing against BTC. There will be many BTC L2s some with great privacy, all interoptable through LN. Ark protocol will have good privacy, there will be many options, each person will choose his protocol and pay/receive through LN.
When that option come, if they are better than monero why would i change?
Until then i use the best solution i know 😉
Ofc you will only change if they are better in your view, but over time if btc keeps being better SOV than XMR, then with more bitcoin acceptance everywhere, you will have less reasons to keep XMR if it's not widely accepted like BTC and with good privacy options on BTC. Until then yes, XMR is probably better for privacy.
And if a better tool borns in the future than both i will migrate to that tool, thats how world works.
All these privacy L2s so far are custodial, permissioned, or require intermediaries (ecash, liquid, lightning, etc)
You can have privacy AND sovereignty with Monero
Using different kinds of money isn't the issue imo.
The issue is friction to swap between them - unfortunately to this day this isn't as simple as it could be (not even close).
That could be easily solved if devs from both sides put the fucking ego away and build together, we would have a much more resilient tools to separete the money from the state
There's also quite a lot of friction in high fees, optional privacy, and tainted coins. All not ideal if your goal is MoE/p2p digital cash
With atomic swaps growing it isn't that inconceivable to imagine a multicoin future where these things are handled by wallets automatically and seamlessly