That started in mid-decade, in the 2010's. Sales really don't count for much now, according to the RIAA. The dominant method of music consumption is streaming, and it has been the dominant method for over seven years. Streaming overtook music sales in 2015. Last year streaming accounted for over 83% of music revenues and music consumption (caveat -- the RIAA doesn't count broadcast listening as 'consumption', only the method through which music creates revenues -- physical sales, downloads, streaming, etc.). This year streaming's share is undoubtedly higher than 83%.
So, naturally, it has to affect the charts. It's why they appear more volatile.