@bdp24
The main reason is price. ASC products are much more expensive. But there are more reasons as well: Effectiveness and sound.
The GIK Soffit traps are broad, and deep, effective in low ranges where it is difficult to get normal acoustic treatments to work, and a fraction of the cost of the ASC tube traps.
I recently went to a show in Oakland, CA which was sponsored by ASC and Pass. Every room heavily treated by ASC tube traps sucked. The midrange was missing and the bass was 1 note. The few rooms I liked either had minimal ASC or used completely different products, like Vienna Acoustics and Fritz Speakers. Honestly this was counter to my expectations. When I saw the traps in a room I immediately expected I would be treated to a great experience compared to a normal hotel room or exhibition hall.
Also GIK is very hobbyist friendly. They have experts who give much better advice than you’d get on Audiogon (including from me!) even if you aren’t going to spend a lot of money. I have never asked ASC for help, so I cannot compare on this dimension.
Best,
E