What's the reason for higher ranked players losing lp for being inactive?

{quoted}

1. it can weed out people who buy high elo accounts. They play games, they get demoted bc they suck. They dont play games they lose their status

2. Once you get to that ELO I think its a lot more important to have to hold your spot in the top 10% of players.

It doesn't do anything to people who get boosted, it takes a while to drop even if you lost every match you played to avoid decay each month.