Why is everyone allergic to telling people prices they paid for home improvement work?

I’m a part of 5 different local Facebook groups where people ask for recommendations for contractors or repairmen. I see countless comments saying they did the same work and refer them to a person or company, but no talk of how much they paid.

I posted a question about a water filter install under the sink, not even to drill through the granite to install the faucet for it. I asked for prices paid, and got 40+ comments with recommendations with similar work done but not a single price paid.

Why is everyone hiding it?