You have a different view of how academia works than most academics.
Most PIs these days do NOT collaborate and are actively hostile towards it. It's a shame, but it's true.
Also, the niche-ing of academia is real, in many fields, there may be only 3 other people on the planet that understand what you are actually doing, and many of them may not speak English and you may not know they are out there until 2 years from now (publishing takes a long time).
Most code is written by grad-students that barely know what a for loop is, let alone how to use git, and they only write it to do it once for a specific paper. Look into MatLab, that is the most used language in bio, by far. It's basically psuedo-code that compiles, and it's still a mystery to most grad-students.
1) test suite - this shouldn't require explanation
2) documentation - both top level docs with examples and well-commented code. keep track of units
3) one-step build - I should be able to download the project, type 'make' (or something equivalent), and start using it