While I agree in the abstract, the problem is that when you're well-established, in most areas, your research basically amounts to supervising PhD students and postdocs who are not well-established. And they're struggling to meet the requirements to finish their thesis, get a permanent position, etc. So if you encourage them to do slow science and publish less, there's a high risk that you're basically letting them down. Plus, to do research you're probably using some grant funding and guess what the funding agency expects...

Thus, most people never get to a point in their career where they can safely say "let's ignore incentives and just pursue this project slowly and carefully". There might be some exceptions. Probably in math, where research is often individual. And maybe in other areas if you can have a smallish side project with other professors that doesn't require much specific funding, or if you have a student who is finishing and has already secured a position in industry so their stakes aren't high. I've been in those situations sometimes, but it's the exception rather than the rule. The truth is that even senior professors seldom have the luxury of not being heavily pressured by incentives.