We will optimize it later, we don't have time for that right now, it seems it works fast enough for our needs right now.

"Later" never comes and all critical performance issues are either ignored, hot-patched externally with caches of various quality or just with more expensive hardware.

While what you say is often true, it is a different problem and does not change the fact of the prior posters.

My favourite quote for that is:

Broken gets fixed, but crappy stays forever