NASCAR Racing: Number of cars per race, sprint cup, cup races

Question
Who decided that only 43 cars would compete per race and why?

Answer
I actually was asked the same question a week or two back, but no worries. NASCAR made it mandatory in 1997 that all Sprint Cup races have 43 cars start, no more and no less. I believe the rule was put into place to add the Past Champions Provisional to make sure a former champion didn't miss the race. This is why at times a lot of "Go or go home" drivers or "Field Fillers" attempt the race, because some teams decide they do not wish to run the event and other teams such as those show up in the hopes of having a better chance to make the race. I hope this answers your question. As to why they don't run more or less than 43 cars is totally beyond me, I've tried looking it up and the only answer I get is what I explained to you.