decreases skills from desynthesis

[OwlBlackX]

There's a cap on how many desynthesis skill points you can acquire. Once you reach the cap, any further increase in skill will also cause a decrease in a different skill, to ensure that you don't go past the cap.
The current cap can be seen at the bottom of the desynthesis skill list (the list that pops up when you click on any of the DoH classes on the character sheet.)

I check mine....

If I max 380skill when it's stop decreases other desynthesis, really?

Since I wanted make all skills same level. Now it's disappointed.... So stupid SE idea this.

[Nezerius]

I check mine....

If I max 380skill when it's stop decreases other desynthesis, really?

Since I wanted make all skills same level. Now it's disappointed.... So stupid SE idea this.

It's only going to stop decreasing if you reset one of them to 0 (which can be done with an item crafted by alchemists). If you remain at the cap of 1160 (which you are, as shown in your screenshot), it'll continue on decreasing a skill, as you increase another.
They mainly introduced this system for the ARR relic, and wanted to incentivize players helping each other by making it impossible to cap every single desynthesis skill.