I think the reason many kids are drawn toward speech and debate is in its team structure; although you get individual awards in things and success ultimately depends on individual preparation and work, some kids, who do not excel in any other area, want to grub for awards, especially if the school has a history of getting prestigious awards.
In my school, Model United Nations is a really big thing as my school almost always wins in local and regional conferences. With a really talented speaker who just graduated last year (to UPenn), he led the team to earn awards on the national level. With that track record, a lot of students join the club, and now there’s like 50-80 people in MUN when it used to be a much smaller group. However, those “joiners”, despite my school still going on a hot streak in winning conferences, do not get a boost in their resume simply because they’re not leaders, but just joiners.
So, my conclusion for this is that speech and debate, like 100% other ECs, depend on your level of depth; there’s a difference in playing the clarinet in your school orchestra and playing clarinet in an all-national orchestra; same for debate. Colleges can ALWAYS distinguish the devoted and accomplished from the joiner status club grubber. This is how they pick who to accept and who to reject. For debate, this just means that a student has to really excel in it for the EC to actually weigh anything. And heck, the president of another school in my area (who always places 2nd, lol) who is really passionate about the club, just got into Yale SCEA. I’m sure the joiners, who would also have the 2nd place in conferences, did not get into Yale.