Great question. I'm not an economist so I have no idea why. The outsourcing rates I've all seen have gotten way higher in the past ~10 years though.

Beyond just the usual inflation?

I'm not an economist either, but I also assume that as the country attracts more local talent for local companies, the competition for outsourcing becomes harder. (i.e, you now have to pay more than the local companies).

All just speculation on my part though, I really have no clue either.