IMO there are (almost) never too many scientists. Yes there will be junk science. In fact most findings are false or offer nothing new. The few that are true form the basis of the progress that mankind has made.

That aside, I think two more reason for the reproducibility crisis are

(1) the restriction on papers lengths by journals. I remember having to cut so much stuff out of my fist papers just to get it down to the 12 or so pages that I was limited to. When I finally finished I thought to myself "I pity the fool that tries to implement this technique based on such paltry information"

(2) Some researchers will not share all material and methods because they wish to stay ahead of the competition. I know this from experience.