A similar number (with significant overlap) have drug abuse problems
There is no overlap, they are in separate categories.
The remainder (out of 10,000) are people trying to get out, and stuck for other reasons, including serious medical issues, mental illness, and abuse.
That data is strange because it separates people into non-exclusive categories. You can be both "extremely mentally ill" and have a substance abuse disorder, or physically handicapped and chronically homeless. The site uses PIT data (Point in Time) which is gathered once a year, on one night in January. This data is unvetted and rather dubious.
The data also in no way implies those are not "chronically homeless" are "trying to get out". Again, all it does is categorize them based on need. This data is useful for figuring out who needs the most services (HUD has said it's the "chronically homeless"1 ), but it's not useful in figuring out who's "trying to get out".