You actually do see this. Queen Elizabeth the 2nd?l for example. It’s more common in “prominent” women. But- the main reason is largely how women and families have been historically handled. Names in most cultures carry through the fathers line. In marriage, it’s much more common in history and even today is more common that a woman would take a man’s last name. So John Johnson and Jane Johnson birth a daughter and she is named Jane. Jane Johnson Jr. marries Steve Stevenson. She is now Jane Stevenson. Her mother is no longer Jane Johnson Sr. And is just- Jane Johnson. The daughter isn’t a Jr. anymore because there is no Jane Stevenson Sr. Which she is descended from and so we no longer need to distinguish the two Janes.
The naming of a son after a father is usually done as a “family tradition” or as part of a lineage, legacy, dynasty. If a man’s great great to the 17th grand father was Joe Marciano- any of his descendants (in a historical wife airs husbands name context) named “Joe” would also be- Joe Marciano. A traditional name. But if a woman is named “Mary Smith,” it is unlikely her married daughter will be “Mary Smith” after marriage, and there may never be another “Mary Smith” in her lineage ever again if none of her defendants wed a Smith again. Mary Smiths daughter weds Pete Greer and has a son- Anthony Greer. If Anthony uses his grandmothers name Mary for his daughter- she is Mary Greer- not Mary Smith.
So it primarily stems from the fact that it’s rare in history and less common today for a woman’s line to keep their family name. Royalty tends to be an exception which is why we number queens. While more women are choosing to keep their family name today- it’s more common in these cases a child receives a hyphenated last name- which is itself a new name- Cynthia Clement- Beckham isn’t a “Jr” to Cynthia Beckham because her mother isn’t a “Clement Beckham.” In cases where a mother hyphenated her name- the daughter might hyphenate and then could be a jr, but the daughter may also choose to use only one family name, in which case she also wouldn’t be a jr.
If the mother decides to keep her family name after marriage or return to it after divorce, and the child is given the same name as the mother and same family name- it’s still more likely the daughter would take a husbands name in marriage when she was of age. Hence overall due to the more common practice of women taking a man’s family name, female “jr’s” and even daughters being named after mothers is less common simply because women are historically less likely to have a “legacy” in that sense where a name and significance of the same name would have meaning. That may change- but regardless in any known practical system where a family name is firm significance and a way to trace lineage, one parents name is favored Ive true other wether or be male or female.
A system of adding the name of each generation to the family name to create a lineage that way becomes very long very quickly. Cumbersome to speak or write and introductions would take forever. Even on societies with similar customers it is common for people to use shortened family names in common use. Combining names like a jones marrying a smith and the two becoming the “Smiones” or whatever- also has issues as the conventions of combining names becomes crucial to identification and in few generations the ability to trace and identify past generational family names from the current one is lost. Likewise it still is simply not the same family name and thus there isn’t an individual line who’s legacy continues. So partly to blame is the social conventions of legacy and nepotism.
Sometimes she's called Elizabeth the Second.