[hgs3]

> Question: is C gaining in popularity?

Did C ever go away? The computing industry is built on C. It is the foundation underpinning everything.

> Are their good reasons to be using C in product development rather than more modern languages?

Even if you use a "modern" programming language you'll be building on C at some level. Linux, Postgres, Redis, CPython, etc. are all written in C. Most programming languages have a C FFI for a reason. It is worthwhile to familiarize yourself with C if only to have an understanding of what underpins everything. Besides, you never know, you might need to write a native Python module or Postgres plugin one day.