Would love to hear more details on how this happened if you don't mind sharing.
I just absolutely do not buy that I took ~5 CS classes and did a great job on the interview questions.
I don't think I did a great job -- but, I was a deeply specialized self-taught iOS engineer who had built a point of sale.
When you're at Google, work is more episodic and less in-depth, so I had a seemingly unusually wide and in-depth knowledge base.
And iOS devs were considered hard to get. And Google had a special focus internally on getting iOS-specific interviewers who, at least in 2016, usually did a lot of work with non-iOS specialists.
So you have these sort of inherent biases towards me seeming relatively impressive to their day-to-day experience with other Googlers. Then, I'm fairly convinced the leetcode problems we do add a significant "luck" portion.
I spent about 6 hours a day, 6 weeks before interviews, in Cracking the Coding Interview and was still missing problems in the 1st chapter towards the end.
I'm selling myself short, probably. But looking back, I see it as luck, structural factors, and what pushed it over the top was focusing on communication / thinking out loud in the interviews. As long as you're intelligent, familiar with the material, and your interlocutor is having an okay day, you'll come off well.
Your experience with interviews and rate of response feels very familiar. Roles I'm definitely qualified for and interviewed well with just not turning out at the last step, and every other variation of it being a dice roll.
I've also applied to all the standard tech companies over the years, but have never once received an interview. I don't really blame them, I'm not some stellar candidate, but I still do it just in case I get lucky. I've had colleagues who couldn't debug a program to save their life (I know because I did it for them) making several times my pay now at the name brand techbro places. I also know some very good devs I worked with at these companies too. I can't say there is anything different about them on average than anyone anywhere else I've worked, so don't give up if you really want to work there. One guy I know finally made it in after nine years of not getting in, and is getting a huge salary, and major recognition for his work, and promotions, so it can happen, just like winning the lottery happens.
Outside the super-compensated roles there often are a dearth of people applying with both 10+ years experience AND competence in the requested tech stack. That being said, the interviews are totally a crap shot. I've had ones where I aced every question and they passed on me. I've had others where I didn't know a lot of what they wanted but they were sufficiently impressed to give me an offer.
Stop thinking about actual ability to do anything and start seeing it for what it is, a game, or better yet, a gamble. You just keep rolling the dice and hope something lands.
For myself, in the current environment over the past two years it's been taking 6+ months of looking constantly doing 1+ hours of applications and interviews daily before I received one or more offers. No cover letter, but spending money on recruiters reviewing and recommending changes to my resume, and applying like a madman at literally thousands of positions on job boards and directly with the company. Have gotten ghosted, gone through five rounds only to not receive an offer, all the normal stuff you hear about.
Generally I've been receiving maybe one or two HR callbacks for every hundred or two hundred applications. Of those HR callbacks maybe half I make it past the tech screening to the first interview. Another half or less I get to a final round. So all in all I've been doing a few hundred applications over several months for a single offer.
If I was really desperate, which I was in the past dotcom and 2008 crash, I would take one of the horrible W2 contract roles that pay barely above McDonalds wages. I've had these sustain me from going homeless for up to a year before I could get something more in line with a regular salaried job at more typical engineer pay. But I'd take those jobs in a heartbeat if I had no other job lined up.
Note I just went to state school with a bachelors, have no top tech companies in my record, am well over 40, and haven't really achieved anything other than getting back up on my feet after getting repeatedly knocked over by downsizing and offshoring.
Good luck, and don't give up. If the Irish can achieve independence after 800 years of subjugation, it's a reminder even in a tech down economy we can find our place in the sun too.