Why does there seem to be more pitching changes in recent years?

If by "recent" you mean "since 2012", yes it's up, but I would say it's just a continuation of a trend that has been going continuously since the 1980s. At least in part due to this trend, in 2020 rules were added that force a pitcher to face a minimum of three batters in most cases before eligible to be replaced. 2020 is an odd year for many reasons, and I haven't seen stats for how the changes have affected this trend.

Jim Albert has a blog with a nice article on historical pitcher usage. One piece that is particularly telling is a graph of average pitchers used per game:

What's the cause, though? Nate Silver has a piece at fivethirtyeight that points out that pitchers are more effective when they only pitch one inning. They can exert more effort for that inning and the strikeout rate goes up. Good for the individual pitcher and that team, but drives the arms race toward more pitchers and especially more relievers.