Then why did it require an amendment to the Constitution to grant women the right to vote?
Strictly speaking, it didn't. In fact women had the right to vote to varying degrees in most states prior to the amendment, and all the amendment formally does is make it so sex cannot be a condition on the right to vote. Prior to that it was up to the individual states to decide who should be allowed to vote, including the rather amusing case of New Jersey which had a wealth requirement but no sex restriction meaning a woman with the means could vote freely, at least until the wealth requirement was removed and the law changed to any male of age.
It's also worth noting that if women "didn't have the right to vote" in any meaningful sense prior to the amendment passing then men didn't have the right to vote until the mid-late 1800s. Because before that most men didn't meet the requirements to vote either, and expanding male suffrage was a major political shift of the 1800s.
Something to keep in mind.
Id literally suggested that some blue state or another should do exactly that if they want to see a conservative court strike down this idea with the quickness. Honestly, I'm surprised it's took this long and the court didn't basically look at it and say "this is designed specifically to make it procedurally difficult to bring to the court - we'll have none of this nonsense."