You don't have to save long term in Monero to spend/receive in Monero

You're confusing anonymity with privacy. Both are important. Coinjoins don't make your transactions private because they aren't hiding amounts or connections. The whole world can still see. You also don't even really get anonymity, just a weaker form of it by way of pseudonymity. Even putting aside the tedium, expense, and time investment of coinjoining - you still end up with weaker "privacy". You're much more vulnerable to mistakes and chain analysis.