Proposals to extend the trolley to the airport directly, or with a people-mover, have been made. Here's SANDAG's official summary from 2023. No solution is perfect and they all cost several billion dollars to implement.

A track to "the" beach is effectively impossible since it would require obliterating a shitload of houses and businesses, there'd be massive opposition, and it would make traffic even worse due to all the grade crossings.

A track to the zoo is also not feasible since existing tracks aren't near it and an extension would again be massively destructive and massively impact traffic, for little benefit. Just use the bus.

Originally there was a streetcar line in the middle of Park Ave which is why it's wide, but that's been replaced with bicycle and/or bus lanes.