The purpose of betas is to test and provide feedback. How many non-developers who install the very early betas are actually providing meaningful feedback (specific reproduction steps, screenshots, logs, etc)?
Has nothing to do with money and everything to do with improving the quality of the feedback. Having thousands of random users submitting garbage feedback just increases the amount of reports engineers have to wade through and triage, which in turn takes time away from actually fixing bugs.
This will improve the quality of the software. If you just want to play around with new features, wait for the public beta.