Having done both, it's simple: you can't have a deep relationship without time. Not just quality time, but quantity time as well. The more relationships you try to juggle, the less you can spend with any single person, and that limits the amount if emotional intimacy that you can achieve.
Yes, yes, love is infinite. The time that you have to be alive, however, is not.
That is even if you intentionally ignore any issues of jealousy.
Idk, I've been with the same monogamous partner for the past 10 years. I'm chillin. No complaints. When I imagine dealing with multiple romantic partners on top of all the other shit I deal with, it makes me want to blow my head off. One is enough.
Excellent answer you shouldn’t be downvoted for. I fully disagree because I’m terminally monogamous, but I have poly friends who are very happy to be poly!