From their perspective, if they qualify to claim you, then they would save money.
Since they did not claim you, I suggest you calculate your taxes again and consider filing an amended return.
It is likely that your standard deduction would be greater, and you will get some money back.
Note: Dependents - If you can be claimed as a dependent by another taxpayer, your standard deduction for 2018 is limited to the greater of: (1) $1,050, or (2) your earned income plus $350 (but the total can't be more than the basic standard deduction for your filing status).
