Many addicts become dealers to support their habit.
Dealing is another story but I don’t believe anyone should be taken to jail purely because they are found holding a small amount of substance.
That system only ensures addicts or light users become jobless violent criminals down the road. Most likely dealers like you said because a drug record prevents them from getting a regular job ever again.
Possession laws also allows cops to plant tiny packages and imprison anyone at will to boost their felony quota (or whatever other reason they feel like)