Today I tried to analyze past rounds on codeforces.
I wrote a primitive parser for the rating changes table and collected some statistics from it.
From the results I realized that rating deflation takes place.
For me it was not obvious, so I decided to analyze more and the tendency was confirmed.


Here are some statistics:
Round #635 (Div. 1): number of participants=1406, av. rating=2170, total change=-11777, av. change=-8.4
Round #635 (Div. 2): number of participants=14830, av. rating=1377.4, total change=-155190, av. change=-10.5

Div2 rounds are difficult to analyze due to the large number of participants, so later I checked recent div1 rounds.

Round #626 (Div. 1): number of participants=788, av. rating=2195, total change=-5689, av. change=-7.2
Round #631 (Div. 1): number of participants=1273, av. rating=2175, total change=-1058, av. change=-0.8
Round #633 (Div. 1): number of participants=1392, av. rating=2161, total change=-14764, av. change=-10.6

From the above statistics, it is noticeable that the number of participants is growing, and the average rating is gradually decreasing.
I think this is due to the ever-increasing popularity of the site (and programming in general). The counting system maintains balance in this way.
P.S. This is not a reason not to write rounds :)

The rules don't say anything about it.