Which can be overloaded by constant bombardment
Which would not be particularly effective if 1) the enemy on the surface has ways of masking their lifesigns so you can't even find where they are, or 2) their friends from orbit come by and fire at you.
Why do you think Starfleet didn't just park the
Defiant in orbit of AR-558, for example, and just let 'er rip?

And how often does THAT happen? The only reason it did in the film was because they kidnapped Geordi and nicked his VISOR.
Just like the transporter.
Much, much, much better to not risk an actual irreplacable life, on either side, if it can be avoided.
Tell that to the starship's crew.
And besides, the very fact that there is an enemy on the surface *for* the ship to shoot at, proves that the UFP must also have surface forces - you can't afford not to have something that the enemy does have. It would give them an advantage, however small.