Most resin manufacturers are run by one or a few persons, often it is not even their main income. It is obvious that there will be a certain fluctuations, i.e. some disappear and new ones appear.
In addition, resin kits, which were really impressive 20 years ago, are for today's standards disappointing. That is already true for some 10 year old kits (the same is true for plastic kits). If a producers does not offer new kits, but mainly older ones, a decline is sales is to be expected - that is even to be expected, if the kits are still have high quality, because it is more likely that a lot of potential customers already had bought that kit.
Your arguments regarding taxes for Shapeway products is wrong at least for most of the states you have mentioned (see the other postings). Anyway, that is not argument against 3D printing, but perhaps that there should be more care not buy only from designers on Shapeways to be not dependent on way 3D printing company.
The much more diversified offer of small resin producers and 3D printing fits anyway much better to the market compared to large scale, high costs plastic kit producers - at least for ship modellers. But I should mention that also in plastic the situation is currently much better than ever before: there also much more and much better kits available. But for sure, at least in my favourite scale (1/700), not from the classical western producers (Revell, Airfix, Heller etc.), but from Chinese and Japanese companies, plus some Eastern European producers. And there are more Chinese companies than Trumpeter, e.g. DreamModels, S-Model, Snowman... The classical Western companies have simply never released something interesting for me or only sold kits developed in Japan (Revell). I would not miss them.