Have you tried it? Check it out e.g. [1].
1) You immediately get to see the date range of the thread. 2) You can instantly navigate to any date or position in that range. 3) Thus, it's not really infinite scrolling. At all. The only similarity is lazy loading, for long threads. 4) On mobile, you also get to preview the comments before actually jumping to it.
[1] https://meta.discourse.org/t/switch-from-gravatar-to-html-cs...