That math doesn't really work out if you think about it critically. If you assume a cost of $1,000 annually as a starting point and a 5% inflation rate, the next year's cost would be $1,050. The initial management fee would be $100. The next years management fee would be 10% of $1,050, or $105, which also happens to match an increase of 5%, which is the inflation rate. The total cost for the years would be $1,100 the initial year and $1,155 the second. $1,155 is a 5% increase over $1,100 if I've done my math properly - yep, my calculator confirms that.
This seems a somewhat rational explanation. It could also be related to needing more accommodations for an aging population or the imposition of additional requirements by whatever governing authority decides we need to do more maintenance/improvements.
On the other hand, I've had years where the increase in MFs has been absent despite inflation. And I do own some TS where the increase is baked in - Buganvilias Resort in Puerto Vallarta, for example, has a 5% inflation rate that is contractually specified. YMMV.