The original marketing of the solvent trap wasn't the problem. The company that started this was preppers discount I believe and they were marketing parts that of themselves were unrelated to suppressors in any form. Although the end result was clear, the ATF was powerless to take any action. The legal responsibility was placed firmly at the feet of the end users should they decide to make the suggested modifications to the parts. Keep in mind that simply being in possession of suppressor parts can be and has been used to prove constructive intent to posess a supressor, although there is no clear line that needs to be crossed. I've been watching this closely over the last few years and knew it would be ending soon because the companies that were selling the parts decided that if selling arbitrary unfinished parts were good, selling finished parts in the form of a ready made kit would be better both financially for them and the end user. Some even advertised sending customers Form 1's for customers to fill out and send in to be approved for their homemade suppressors. The fatal flaw in this action was that individuals are prohibited from possessing suppressor parts prior to the Form 1 being approved. Simply having the finished parts with the clear intent of the end result violates NFA regulations both from a retail standpoint and individual end user standpoint.
Anyone can build their own suppressor following Form 1 approval and many have, but a manufacturer must serialize and Form 2 any and all manufactured firearm and NFA related devices and are prohibited from transferring them to anyone accept other SOT dealers without a Form 4 approval and subsequent stamp issued to the end user. One of the companies ordered to cease was a class 07 manufacturer. Im not sure how they thought they could do this in clear violation of their 07 license requirements. All of these companies overstepped the NFA regs attempting to circumvent the process. It was only a matter of time before the ATF put an end to it.
For the record this information isn't an opinion of mine supporting the ATF but merely explaining what I saw happening and predicting the inevitable outcome.