I wonder why it took so long for Western governments to take measures to develop/buy rapid test kits for Cov-19. Is there anything charities can do about it - now, or in the future?

I checked this question, but, despite being the first idea, there was no feedback concerning RDTs.

First, RDT has been an important tool against other epidemics - HIV, ebola, zika, etc. Second, it was part of the contention strategy in Asia. If you can identify infected people quickly, you can respond way more effectively. Third, safe vaccines and treatment take a lot of time to be developed, and are often invasive. Not RDTs.