US plastic kit manufacturers were in steep decline before the rise of the Chinese manufacturers. By the early 1990s, US producers were hardly releasing anything new. The most dynamic producers were the Japanese, but also, for example, the Czech and Polish producers.

The Chinese tariffs had nothing to do with the decline of the US producers.

Tariffs would not help to restart the business in the US because the US market alone is too small for plastic kits. Plastic kits are only cheap if they are produced in large quantities, so they have to be exported. A manufacturer in the US would have three disadvantages: a location with very high production costs (e.g. there is no chemical industry to speak of to produce the plastic), no free trade agreements but tariffs everywhere, and a shrinking market in the US due to the demographics of US modelers. And if modelling gets more expensive in the US, the market will shrink even more.