As Bitcoin_BOy$ said, there is also a trust part. Even if the individual wallet is developed, it must be accepted by the bitcoin community.
Actually I don't agree with the trust part. Trust is earned over time, if any developer gives up because he has no history and no trust, development is over.
Also everything is open source and if it is good, it will get peer reviewed, you can see this on GitHub in the number of "Stars" and "watchers" and "contributors" and some other stuff.
Yeah, everyone may not trust a new wallet initially until others have had the time to inspect and audit the code, but this shouldn't discourage development. Trust comes with time and if the software is built well, you should be able to gain trust after some time as long as the code is open source.