It's funny to me how folks always focus on the Tie Fighters in my collection and yet there's just as many X-Wing Fighters that never get mentioned. No love for the Rebels, huh?
Anyhow to answer your question...
The reason for the number of Tie Fighters is simple:
Some folks are army-builders of "trooper" action figures. (I am)
Some folks are collectors of package variants (I am not)
Some folks keep the packaging for most of their toys (I do)
Some folks like to display their stuff loose (I do not)
The point is, collecting comes in all different kinds of styles and mindsets.
Suffice it to say that despite my age (40), I still collect STAR WARS toys like an 11 year old kid hoping to one day re-enact the movies in his bedroom.
I just really took "We count 30 Rebel ships, Lord Vader!" literally!
Besides... having ONLY ONE Tie Fighter or X-Wing or Snowspeeder in my collection just seemed... wrong to me. Some ships need to be in squadrons, bay-bay!!!
The UP-SIDE is that certain STAR WARS vehicles (Luke's Landspeeder, Sandcrawler, Millennium Falcon, Darth Vader's Tie Fighter, Slave I, etc.) DO NOT appear in the films as squadrons or in large numbers. So I was quite content to simply buy ONE of each of those vehicles for my collection.
The same holds true for armies. Yes, there are 500 Imperial Stromtrooper action figures in my collection (it's insane but true).
But there is also only ONE Chewbacca figure in my collection. There is only ONE Darth Vader. There's only ONE Han Solo, ONE Luke Skywalker, ONE Princess Leia (in each of their various OT outfits). And of course, there are only ONE C-3P0 and R2-D2 in my collection.