Tatooine... There's no evidence to say Speederbikes AREN'T in-use on Tatooine besides not seeing biker scouts in the film... The troops out in the desert we see on a patrol and we see deployment via drop ships/shuttles... I'd rather take a short cruise in an A/C shuttle than a long ride out to the dune sea on a bike...
That's not to say that routine patrols for the outskirts of settlements, or that patrols between homesteads aren't routinely done with a Biker Scout team, to maintain the peace.
I buy absolutely NOTHING about sand damaging equipment. It didn't damage swoops or land/air speeders, so speederbikes wouldn't be adversely effected either... Or so one would think, despite what some half-assed EU maybe says.
Hoth... Supposedly Hoth did have the support of some Scouts, however where would they be effective?
On an open field, a speederbike would be a riper target for anti-infantry fire... The bike's are relatively fragile, and unshielded for the trooper aboard... The vehicle's armament is weak at best as well, it's not an offensive weapon in the slightest, but as the name implies, a speederbike is the tool of Scouts and Couriers/Liasons... It's fast, maneuverable, and that's about it. It's good for patrol or pursuit of someone, but not for mainline fighting.
If they're used on Hoth I'd assume it's either that they're used sparingly or they're used to simply keep flanks clear of possible ambush... Or possibly to eyeball visually anti-armor traps such as mines or whatnot that the walker's sensors maybe aren't able to pick-up... They're not front-line fighting, but maybe flanking the approaching walkers/armor to make sure it doesn't bite it on some well-layed prparations.
Endor... Where we actually see Speederbikes in the film, we see them doing the job they're designed for. Distant patrol.
I've always held that the film indicates that the Alliance saboteurs land VERY far from the main complex the Empire has built... The complex, an area of many miles deforested and fortified with anti-air, anti-armor, and other emplacements to protect the shield dish, is the goal of the strike team, and they've got a hike to get there... The Empire's protecting outwardly with roving random Biker Scout patrols in teams of two. They have the bikes to cover the distance from their base to their scouting points, and they have to not really engage the enemy but instead report the enemy... As Luke himself warned Han to be quiet as their warning the main base would hose the operation. He also pushed early for jamming the coms of the Scouts he and Leia engaged, forcing them into battle instead of running away to tattle.
On Endor, the trees are a threat or hinderance to every weapon the Empire has really... Only the basic soldier has an advantage... AT-ST's fall prey to the traps the Ewoks had worked on (presumeably) in advance for some time, planning some kind of fight with the Empire on their own that just gets caught up with the Rebel Strike team when they meet them... And AT-AT's are simply hindered by not being able to have clearer lines of sight to the ground for targets, or simply moving in the trees, so they're relegated to the deforested area where (ultimately) the Empire expects the attack anyway on the main complex. The ST's have to move with caution to be effective due to the trees.
So that leaves the Speederbike for scouting and security. It works too... The bikes seem to be easy to handle to avoid the trees, especially with expert training which one can assume the Scouts have, and not to mention that they don't expect to be pursued, they'd simply have to return to their base and make a communication that they've made contact with Rebel forces.... For that, the bikes seem to work well. Luke/Leia both handled speederbikes like pro's on Endor too, just on a whim, so they mustn't be too difficult to deal with.
If you're doing just simple patrolling and if your mission profile is to not engage but to return to base and report contact, then I think the speeder bike's the ideal tool for the job.