Only intellectual stat decaying too fast

What is the Intellectual skill level versus the other skills?

From the wiki https://rimworldwiki.com/wiki/Skills :

Beyond skill level 10, XP points are continuously drained away. A skill level is lost only after falling to 0 XP points, and then losing a further 1000 points, preventing repeated level loss and gain right around a level threshold. Experience decay is strictly calculated based on the current skill level and is not directly affected by skill use; Instead, gained XP simply cancels out loss, and vice versa.

XP decays at an accelerated rate with higher skill levels. This means that all XP earned after 55,000 total XP (level 10) effectively has less value, especially for skills that a colonist does not use frequently, because it will disappear. In most cases, XP is gained by time spent on a skill, and not by effective work performed: Working faster does not make it easier or faster to gain XP, or compensate the decay loss. Level 20 (max level) is very difficult to acquire, usually only achievable by colonists solely dedicated to a single profession.

The Great Memory trait halves the skill decay rate for a pawn.

In addition, at a certain point, having a skill with zero passion will earn xp at the same rate as it loses, meaning it would be next to impossible to get a pawn to level 20 in that skill unless you dedicate every waking hour to it.