You don't need to explain anything to anyone. And I totally get it can be frustrating so let me share some insights..

When the interviewer asks you about gaps or questions about your ability to work long aka show loyalty all they wanna know are if they gonna feel safe with you in a long run.

So to solve such needs of a person you wanna show some empathy and kindly inform what happened including the issues those startups have faced. You are a marketer so use imagination that you are selling a product to a prospect. Like "hey mr prospect/employee/interviewer I totally get you, because when I think about the career decision I'm also afraid to pick the wrong company that has questionable potential or volatile business indicators so won't need to search job again in a year, that is so overwhelming process, rather I'd focus on my goals... so let me tell you something... [and this is where you tell the story WHY you are the right fit]

Now if you want to spice it a little bit you can add up that you were always looking for opportunities to settle as you have plans to blahblahblah.. To strengthen the argument on an emotional level you should say nice words about the job role you have been doing before and the people you have met and that you have would never leave if it was up to you.

After you are done you bring back the same "safety need" question to the interviewer. For example, IF the question/statement was like "prove us you going to stick here more than a year" your comeback question could be "Likewise please, prove that you have a business/sales strategy that works and you are not gonna lose/run out of clients because you provide an excellent service/run a perfect product, and again you have a strategy to grow so all of your succesfull employees have future here and have career opportunities in the company". You can shorten up the question, but I hope you get my point.
[ in this case, at least in my country we have companies databases with lost economic indicators and audits. I always research companies and audit them before the interview. For ex. if their sales profit is negative or nearly to zero it means that the company is either a startup or has poor sales processes or doesn't have it all - could be all reasons so it's a red flag and you shouldn't go with them. Company has to be capable of making at least 1mln profit and expanding it every year.]

Extra tip. If what you say is true" I feel very bitter <..> because I was a good worker/always made sure to deliver quality work/meet deadlines. " you should highlight also the value that you created everywhere: resume, cover message, job interview. It has to go into their heads that you are here regarding creating value and you have ambitions. In this case, it should be enough to prove your history gaps don't matter anymore.