Is there a reason why abilities like static or flame body aren't banned? I was just wondering since I remember abilities like Sand Veil being banned before
I can actually answer this one a bit more in detail since I was around in DPP-era, when this was first introduced (Sand Veil ban). lyd and Felixx did well with answering, but I wanted to add more detail to this since it's not really a question often asked.
There's a few things to consider with Static vs Sand Veil. First and foremost - Static does not affect the accuracy of moves. This alone is a huge difference. While Stone Edge only has an 80% chance to hit Zapdos (assuming 0 evasion), it will always be 80% assuming its item is not anything like Brightpowder. Furthermore, Static and Flame Body only work on contact moves - any moves like Ice Beam and said Stone Edge ignore the properties of these abilities. In other words - we have an ability that assumes a specific circumstance (contact) and only has a chance to activate. Discharge and Lava Plume have roughly the same percentage of their effects as well, and the only time these won't go off are circumstances with immunities involved (Lightningrod, being an Electric-type, Flame Body, being a Fire-type).
Sand Veil introduces a more complex scenario. See, back in the previous hay days of Gen 4 Garchomp was able to abuse Sand Veil quite a bit because Sand was permanent and it was a rather dominant force in the DPP metagame. A single miss could easily swing the battle in the Garchomp player's favor because it was also easy to fish with Substitute and, if you were a total dick, Brightpowder. Garchomp (and then Gliscor) at the time were fairly hard to kill - your reliability was banking on Ice moves (and praying no Yache Berry), but when that only works 80% of the time (or worse with Brightpowder) and you factor in that Yache Berry allows Garchomp to survive an ice move, it makes things very troublesome. For Gliscor it could abuse some of its defensive bulk by sometimes banking on a missed attack here and there or having an easier time passing with Baton Pass.
While luck is (unfortunately) an element of battle, you have to understand that circumstances such as Sand Veil are very different from Static / Flame Body. They assumed more strict conditions than Sand Veil at the time and made it a key factor in banning Garchomp as well. Nowadays this is somewhat less of an issue since sand isn't permanent and there is a possibility of rain as a playstyle (and Zard Y for Drought), but the counterplay for it back in the day was much harder to handle.
Nowadays Sand Veil isn't really thought of much - sometimes it can bail you out of a weird jam, but most of the time you'll want other abilities on Pokemon that used Sand Veil anyway (Gliscor for Poison Heal recovery, Garchomp to chip at contact Pokemon).
