Because the NRA owns the Republican Party. Goggle " has your US congress person received donations from the NRA" then scroll down to the web results. click on any state and you will see its 95% Republicans.
Can you explain why the Democrats rejected 2 Republican proposals on gun control yesterday?
Note: you don't understand this issue, or really care to understand it. You're "for" something because the NRA is against it. No other reason.