Over the course of the last decade, each year has seen an average of 2,685 new laws - the equivalent of almost seven and a half a day or one every three-and-a-quarter hours

https://www.theguardian.com/politics/2007/jun/04/houseofcommons.uk

This was in 2007 in the UK. But I imagine it's much the same in the US. Literally impossible for anybody to follow every law, but that doesn't matter because as you say they're selectively enforced