Very rarely have I heard an engineer look at a functioning piece of software and go “let me rewrite this because it’s not a language or framework I am familiar with and fond of”. If that does happen, it’s usually inexperienced (or bad) engineers.

Rewrites usually start with a gap in what is available and what is needed: missing functionality, existing frameworks getting obsolete, difficultly maintaining code because of the existing implementation complexity, costs, scalability issues, compliance challenges, etc. Most of these things serve the business more than the engineers.