Why no Zats or Staff Weapons in Atlantis?

[StargateMillennium]

The P-90 has a firing range of over 5,500 feet, admittedly with an effective firing range of 650-ish feet at fifteen rounds per second.
Staff weapons are mostly hip fired, don't seem to have a sight and fire seemingly once per two seconds.
If you want to blow a hole in a wall use a staff weapon.
If you want to shoot dudes use the P-50.
If you want to do both, take a P-90 and undersling a grenade launcher to it.
That said... we don't know how many shots you get with a staff so it might beat the P-90 in having lug around ammo.

Having an automatic weapon also is an advantage. You can spray in the general direction of your target. Firing in bursts is a form of spraying at the target. One shot might miss but another might hit. The slow firing staff weapon makes it hard to hit enemies that shoot back (might be a good hunting weapon). If the staff misses, all the jaffa can do is take cover and wait for it to be able to shoot again.

The other weakness is bulk. The staff weapons is huge and clunky. You'd have to carry a lot of P90 mags before getting the bulkiness of a staff.

[LionHamster]

No episode images show the Atlantis team using zats, and there's no mention of them yet on SciFi's Atlantis site's tech section. They may have left zats out of Atlantis. For the most part, Atlantis won't deal with the Goa'uld, so in order to all new viewers to get into the show without having to know the history of SG-1 (namely, what zats are), they chose to exclude zats from the show.

Acctuly when they took atlantis form the reps they used zats while still in the sgc