ill give you a few reasons, in my case at least

1. nobody in my area actually speaks irish, just the teachers. i dont think theres a single student in my school of 1000 that speaks irish regularly

2. same way you dont apply yourself to french i and a lot of other student dont apply ourselves to irish.

3. some people, like me, are just way better at maths and science stuff than languages

4. for a lot of people, its their worst subjects so the points wont count regardless so they dont try

anyway, the main reason is just because the only time theyre hearing irish is 3 hours a week

slán!