As usual in aviation, you cannot make a decision without impacting a lot of other stuff, this case is no different.
For example, on certain aircraft models with limited OH space, a number of luggage OH bins - especially towards the extreme ends of the cabins as that is where the FA stations are - store emergency equipment as well.
If you decide to lock the bins, then either you have to sacrifice OH space and reconfigure the bins to move the emergency equipment to exclusive bins, re-certify the plane (as it involves emergency equipment) and re-train cabin crew to never store any emergency gear in the other bins. Or, keep the bin configuration as it is, but don't lock the ones storing emergency equipment while you lock the others, and face a situation where pax in the extreme ends of the cabins - where emergency exits happen to be as well - can still get their stuff, which may encourage others to pry their bins open and lose a lot of time.
For example, on certain aircraft models with limited OH space, a number of luggage OH bins - especially towards the extreme ends of the cabins as that is where the FA stations are - store emergency equipment as well.
https://i2.wp.com/thepointsguy.com/wp-content/uploads/2018/1... - an extreme example on Delta to prove the point, usually they store smaller emergency items.
If you decide to lock the bins, then either you have to sacrifice OH space and reconfigure the bins to move the emergency equipment to exclusive bins, re-certify the plane (as it involves emergency equipment) and re-train cabin crew to never store any emergency gear in the other bins. Or, keep the bin configuration as it is, but don't lock the ones storing emergency equipment while you lock the others, and face a situation where pax in the extreme ends of the cabins - where emergency exits happen to be as well - can still get their stuff, which may encourage others to pry their bins open and lose a lot of time.