They could, and did.
"Now why is that?"
Because activist U.S. Supreme Courts have used the 14th amendment to apply the first amendment to the states in addition to the federal government.
"Especially if the 1st Amendment was originally implicitly intended to protect the rights of white male landowners"
You need to reread it. The first amendment protected the freedom of speech, press, and religion for all persons. The right of assembly and the right to petition the government were protected only for "the people" - white, male, citizen landowners.
Care to detail how the Constitution differentiates those two groups?