A lot of it, given the comments I see in relevant threads, comes from the inefficiency of every electron app having its own copies of node and chromium in memory (and on disk, and being transferred over the network when installed/updated, though those are smaller issues than run-time performance). Though that is unavoidable given how it works unless particular LTS versions can be enforced so everything is tested against those making sharing easier/possible. I'm not sure how much of an issue it really is anyway: how many people are running several instances of Electron applications at once?

Also I get the impression that a fair amount of it comes from people who are parroting what appears to be a popular sentiment, without actually understanding or having skin in the game! This says something disappointing about technical communities.