And it will use 1TB of ram to run.

Because the plugins embeds into existing native applications and uses existing native SDKs.

Audio software has strict buffer/latency demands which usually cannot be guaranteed on interpreted language platforms.

Doing audio synthesis with JS or any other interpreted language really is totally possible and has been done in a more or less serious way in several implementations and webtoys etc. But if you need extremely low latency and guarantees you cannot go that route, sadly.

There are few reasons: - they most of the time run embedded in a DAW - they are usually computationally intensive themselves - they are meant to be instanced as far as memory/CPU can go

ad to the third point: Music producers already require and use pretty powerful rigs: 32-128GB RAM is not uncommon, CPU as good as it gets. There's great benefit when you can run 100 instrument synthesizer instances parallel vs 14 instances - it's a difference between a differentiated orchestra and a rock band.