Some people do not place the same importance on arbitrary described holidays as others, nothing right or wrong about it, just the way it is.
Plenty of people, myself being one of them, see nothing any more or less important about Mother's Day, New Year's Eve, a birthday, anniversary, etc, than any other day of the year.
Being a parent is important,Mother's or Father's Day is not. Being married is important, an anniversary is not. Being alive is important, a birthday is not.
Your husband called his mother on Mother's Day, and that ought to be sufficient.
If he is otherwise a good and decent man and husband , keep him. If he is simply a bad human being or a terrible husband, his buying a card from Hallmark would not make much difference.
If Mother's Day is important to you, make sure your children know that, and if you want your husband to do something specific, TELL HIM SPECIFICALLY WHAT YOU WANT HIM TO DO!! Do not hint, do not wait for him to figure it out, do not think it should be automatic, do not assume he should wish to do it without prompting.
You are an adult married to an adult, both of you are allowed (and encouraged) to speak up about what you want. Neither of you are allowed to get annoyed because the other can not read minds.