To add a little further context to Buffy's and Pete Clark's: in the U.S. in the current state of things, as I see in my own math R1 state univ (I'm on grad admissions), the total number of (EDIT: not admissions) applicants is perhaps 30% greater than usual. At the same time, economic constraints (partly due to uncertainty about the course of the pandemic) are reducing the number of offers we can make, and also reducing the volatility we can tolerate in the outcomes of offers made.
Further, the partly-good idea of the April 15 common date (in the U.S.) for commitment to grad programs tends to make us prefer to make offers to (good) people who've given some indication that they'd come to our program if we made the offer. E.g., at least some explicit mention of our university and some relevant people on our faculty. Otherwise, we figure we're just a back-up, and the April 15 thing has game-theoretic implications.
So there's a confluence of complications in this cycle.
EDIT: currently, as ever, contacting potentially relevant faculty by email is some evidence of your genuine interest. But/and this should be clear in your statement of purpose. If you don't get a first-round offer from a school, you can tell the Grad Office (in that dept) that you still are definitely interested in being on their "wait list" (or whatever they call it). And follow up again on April 14... :) Of course (!!!) if you send spammy-sounding emails, it won't help at all.
EDIT2: and, as Noah Snyder comments, international students may cost a department more in terms of the budget-games of tuition, and may create complications in terms of English fluency for functioning as teaching assistants. The other current features amplify these aspects in an unfortunate way.
I should also note that at my univ the math dept is NOT allowed to claim that we cannot cover all the math courses, due to reduced personnel (hiring freeze on faculty, for example). So we really need all new grad students (if not on fellowships or RA's) to be able to "hit the ground running" in terms of teaching. English problems are very unhelpful.