I think the ship has a very strong presence in Season 1
It does for sure... and the movie even moreso. 2008 would've been a better time to look at this (as of right now... it can come back at any moment). But, season 1 is done, as is the movie.
and regardless of that there is very little actual correlation between screen time/show prominence and probability of being released as a toy.
Not according to Hasbro, and especially when it comes to bigger items.
This is why we get some no-name Mandalorian Guard before Suchess Satine. This is why we get the Shadow Arc over the Solar Sailer.
Poor examples... You get the Mando Guard because he's more interesting and sells better than female characters. That's a proven track record Hasbro cites time and again. I think you may get Satine, but Hasbro's pretty staunch on the, "female characters don't sell" point of view and in general they're right... especially where kids are concerned. They'd rather put out something people are more inclined to buy (and buy multiples of at that), than a female character that may be a tough sell regardless of her prominence in the series.
You got the Shadow ARC because it's already tooled and the hoped-for sales of that were planned to help push new tools in that deluxe vehicle line-up. And the Solar Sailer is anything but "aggressive". Look back on their commentary there in the past as well. Look at the Cloud Car coming up. It's made into a road-warrior vehicle with tons of hidden weapons and things because the vehicle was (for many years) declared "not aggressive" by Hasbro. The Solar Sailer would be "boring" to many, again (and especially) kids I think, even though it may appeal to me (especially if it were done to-scale, it's not really that large with the sail down and I love that ship too).
Better examples are looking at the Y-Wing, the AT-TE, and the seemingly dropped plans of the Turbo-Tank... The Y-Wing had a huge story-arc where they were prominent and popular. The AT-TE's appeared in Season 1 and 2 a good bit. The Turbo Tank was (supposedly) planned to be more prominent in Season 2 and for some reason wasn't, but Hasbro seemed to have thought it would be. So TV prominence seems to generally play a large role in why things (especially big things... comparing figures in and of itself isn't even fair to do) get made.
The tooling dollars become increasingly more costly the bigger and more complex the toy is though... so that's why it's not fair to compare why you don't get a Satine over a Mando guard, with comparisons of why you don't get this vehicle over getting that one. They're really whole different balls of wax, and the reasoning why you get one thing over another changes with each.
I'd add again too, that the AT-AT isn't marketed to adult collectors who ONLY collect Clone Wars too...
It's marketed to:
-Adult collectors... period. But especially the OT crowd which dominates the adult collecting community.
-Kids, who just see a big assed walker for their Clones that stomps, makes lots of sound, and which towers over even their beloved turbo tanks and AT-TE's and such... Kids don't know (or care?) about the AT-AT being from a 30 year old movie, they just know their clones will look badass in it. It's a clone walker.
Really the vehicles overall have been pushed for cross-over collecting more than anything else. Hasbro can't really afford to differentiate too much with those, even in the $25 range.