None of those are 'big reasons'.
Or rather, they might be 'big' for a few teams in specific areas, but they are not 'big market opportunities' not even close.
The ability to go from Java+Spring OR Perl/PHP - and then have the choice to actually do JS on the server is a big deal - and that's why Node.js was a success.
The sandbox is nice but I don't see it being a big opportunity just yet. 'Running your own SaaS with untrusted code' is a developing area, and I'm not sure of Deno actually is a solution (how does one integrate with it). Also - Node.js does have some options there in the form of VM2. The real security hasn't been validated just yet either.
'TS first' - I think is just a toolchain and packaging optimization. We're all going to be running some kind of process for bundling and packing, it requires no effort to transpile in to JS at that point.
The isomorphism again, is a neat feature.
In other words, Deno has some cool new features in the context of 'the market/users space' for server side JS, whereas Node.js actually founded and created that entire market category.
Under normal circumstances, I wouldn't bet on any movement towards Deno, just because there are too many legacy Node.js already there, but since there seems to be a strong fanboy following, I don't doubt a lot of young devs push for it to be used because it's cool and shiny. All 'shiny new toys' have some benefits here and there, it's just a matter of contextualizing them into the incumbent landscape.