Ding didn’t play all that many tournaments before becoming World Champion either, so maybe not a huge surprise that he continues to play little. His tournament results over the last dozen months are +2-5=15 with a tournament performance rating of 2692. If one includes also match play it is +5-8=23 and 2732.
Even Carlsen played fairly little in classical lately (even if he did play a lot of online/speed chess events). Over the last dozen months he has +19-4=22 and a performance around 2810 in classical, which is unusually low for him, and with unusually many losses.
Ding Liren keeps withdrawing from events, now for the fourth time in a row over the last five months. The previous were speed chess online or OTB, but this one was classical chess:
https://www.reddit.com/r/chess/comments/16ock4y/the_newly_appointed_world_chess_champion_ding/
It is suggested that Ding now will not play the following events he had signed up for, S:t Louis rapid and blitz, and Sinquefield Cup, in November/December. Will he play again before the next title match? Will he even play the next title match?
Matches can be taxing, but Carlsen’s toughest was probably Caruana at the end of 2018, and the year after the match he played:
World rapid championship 2018
World blitz championship 2018
followed by all the classical 2019 events
Tata
Gashimov
Grenke
Norway
Zagreb
Sinquefield
Isle of Man
London Chess classics
Norwegian League games
A bunch of rapid/blitz OTB
Lindores Abbey
Côte d’Ivoire rapid
Côte d’Ivoire blitz
Norway Chess blitz
S:t Louis rapid
S:t Louis blitz
Fischer Random World Championship
Kolkata rapid
Kolkata blitz
World rapid championship
World blitz championship
and many online events, a few of which were
Svidler match online
Banter blitzes
Titled Tuesdays
Etc
So Ding Liren is being unusually inactive for a World Champion.