SPG has over 1500 properties and MR has over 5200 properties. If you assume that the average tenure for a hotel GM lasts ~10 years (which might be on the high side) that means that on average over 600 GM positions open up every year which is approaching 2 GM openings per day. Just counting the SPG properties alone averages to 150 GM openings per year.

Change at the GM level is inevitable and I don't think the data points presented upthread indicate any particular trend.