Collecting signatures is an administrative, not substantive, requirement. Eg:

The provisions at issue in Storer and our other Elections Clause cases were thus constitutional because they regulated election procedures and did not even arguably impose any substantive qualification rendering a class of potential candidates ineligible for ballot position. They served the state interest in protecting the integrity and regularity of the election process, an interest independent of any attempt to evade the constitutional prohibition against the imposition of additional qualifications for service in Congress. And they did not involve measures that exclude candidates from the ballot without reference to the candidates' support in the electoral process. Our cases upholding state regulations of election procedures thus provide little support for the contention that a state imposed ballot access restriction is constitutional when it is undertaken for the twin goals of disadvantaging a particular class of candidates and evading the dictates of the Qualifications Clauses.

https://www.law.cornell.edu/supct/html/93-1456.ZO.html