Having a current employee add your resume to an ATS as a referral is the most efficient route. Around SF at least it's not particularly hard to find someone willing to do that even if they hardly know you. This sort of networking is likely harder elsewhere, but perhaps not by much.

Simply uploading your resume to a large tech company's website will rarely get you anywhere, is what I've heard from recruiters.

Ah, so that's what I've been doing wrong for 18 months. Thanks! I'll be putting this to good use :)

Second this. Internal referral is the most reliable way to get in the door in my experience.

Most likely you either don't have 5 years of professional experience or they are filtering you based on visa/citizenship status. The industry is very broken.

The recruiter just reached out to my LinkedIn profile. My understanding is it’s really easy to get the interview

Your profile must have been pretty solid to get those interviews though. In my experience, just having some proof of knowing Python scripting is not enough. Would you mind discussing the other pieces of your background that you think may have helped in attracting recruits?

I almost wonder if throwing “leetcode” in your skills section would get you interviews at these companies...