With startups, you can pivot (with academia you can too, but it's rather 3-5 years).
With startups, you can fail (and try again); in academia, if you fail, you fail.
In short: with startups, if something is not working (or you totally lost belief in it), you can quit a project without quitting startups for good. In academia, if you want to stay, you often need to stay in a miserable conditions 1-3 more years (e.g. to finish PhD, postdoc, etc), just not to get kicked out for good.
Moreover, with startups, you can start your group being 20, without anyone's blessing.
With startups, you can fail (and try again); in academia, if you fail, you fail.
In short: with startups, if something is not working (or you totally lost belief in it), you can quit a project without quitting startups for good. In academia, if you want to stay, you often need to stay in a miserable conditions 1-3 more years (e.g. to finish PhD, postdoc, etc), just not to get kicked out for good.
Moreover, with startups, you can start your group being 20, without anyone's blessing.