They’re not part of the Republican coalition. Sure, they mostly support Republicans, but the NRA is a single-issue organization. They don’t owe it to you to lend support on non-gun related matters.
Aside from endorsing at least one Dem with an anti-gun track record, they need to wake up and smell the coffee.
Insurance, health care, environmental issues all affect the RKBA in practice, especially when the health care issue is over state-provided care.
Votes on those issues can affect the RKBA as surely as an attempt to repeal the Second Amendment.