[AKADriver]

I think the issue with your repair isn't the adhesive itself - an MMA (methylmethacrylate) adhesive like you used should be even better for plastic than a CA (cyanoacrylate aka superglue) based adhesive like the tech-bond - but that for that type of adhesive to work you'd need to have a patch/filler material pressed into the crack, just the way that stuff cures it won't work being filled into a butt joint. If anything the MMA is actually too reactive with the plastic to be used to "coat" a plastic repair the way you can with CA.

My guess is even though CA makes a weaker bond on plastic fuel tank materials than MMA, tech-bond supplies CA in their fuel tank patch kit because it's easier and safer to use and good enough for an unpressurized tank, and because like I said you can spread the viscous CA adhesive they supply over the finished patch as an "armor coat".