There are so many reasons why this could be.
I see you.
To those like me who it's been a very painful "holiday" because of a strained or non-existant or acrimonious relationship with your own mother, be kind to yourself tomorrow.
I used to feel ill when looking at cards that I felt like I needed to make/purchase. There's no greeting cards (though in this era maybe there finally is now!) where it says "Sorry I was your biggest disappointment." or "Yeah, sometimes I hate you too, bitch." or "I know that nothing will ever be good enough, but now you can tell your friends you got a mother's day card too, so let's pretend it's a nice one and call it good."
I've been lucky to be able to have kids by choice (not because I felt I needed to, and my biology was cooperative, I realize that is fortune rather than anything else). It's nice to get a homemade thing or to go out to dinner, but I worry about all the kids pressured to do this shit at school who grew up like me, or who had an absent parent. So even then, it's always been a day that's uncomfortable. I don't think my kids should be grateful because I got knocked up or kept them alive. If they don't think about that at all then I'll consider that a success.
So today and tomorrow I'm trying to not to think too much about the person who I'll never be good enough for (they've told me as much for almost a half century now, haven't changed their minds and I assume will not in the future). But for all the people (regardless of gender)--lovers, friends, teachers, kind strangers, mentors--who have been there to help guide me and shape me in a positive way. Especially for those who have shown me that there isn't just one way to be feminine, a woman, or a parent and that I'm okay. Who did not take advantage of vulnerability and instead of attacking were nurturing. Who have definitely helped me learn how to give and receive grace better than I would have otherwise, something that has helped me not to rip up my children like I was ripped up. Some of you are even here, who helped with that and you don't even know it--maybe someday I'll have the courage to tell you.
You don't need a nice, kind, or nurturing mom to be worth a damn, and if yours couldn't see that precious in you, human to human, it was really them that was broken, not you. You are absolutely worthy. And if you've nurtured others, regardless of if it was as a parent, friend, partner, teacher, kind stranger, or mentor--thank you. Especially if you feel like that care and love goes into the void. Not that it doesn't suck if you don't see what happens as a result...but it's not wasted. Thank you.