Aside from developers keeping their identities private, their project needs to be as decentralized as possible. Samourai had a single point of failure which is their centralized coordinator. In contrast, with Joinmarket there isn’t a centrally controlled server that interacts with participants. They could still decide to target Joinmarket but it would be a much weaker case.
As reminder, Samourai team introduce decentralized Whirlpool last month. But unfortunate the founder got caught when it's not "mature" enough.
If the devs want to take credit for their work and earn money, they need to have public identities. Otherwise businesses would stay anonymous too. One can simply not stay anonymous and own a business at the same time.
The problem is the tax system. Once you start paying taxes, they already got you. Now you are taking orders from your biggest business partner, the government.
Imagine a dev, doing all the hard work, fixing bugs and shit but in the end he gets nothing because he stayed anonymous. How many people are willing to take this? Not everybody is a saint like satoshi.
Theoretically an anonymous developer could ask for donation or funding. But only few people would make donation and that anonymous developer need to gain trust for some time.