Why is Santa Claus a man but Santa Maria a woman? [duplicate]

The city names you quote are all derived from Spanish, where "San" (or "Santo", as @tchrist clarifies below) is the male inflection and "Santa" the female one. However, Santa Claus isn't derived from Spanish, but from Dutch, where it was originally rendered as Sante Klaas, and was modified to Santa when it was adopted into English (and from English, to the rest of the world). Here's Etymonline's take on it:

from dialectal Dutch Sante Klaas, from Middle Dutch Sinter Niklaas "Saint Nicholas,"

English, like all other languages, borrows words from many sources, and they often carry over remnants of their original grammar or usage, even when it makes for inconsistent usage in English.

You can check the following links for references.

Sinterklaas (Wikipedia)

('Saint Nicholas') is a traditional winter holiday figure celebrated in various regions of Europe, including: the Netherlands, Belgium and Luxembourg, some parts of Germany and Austria, (Sankt Nikolaus); Switzerland (Samichlaus), Italy (San Nicola in Bari, South Tyrol, Alpine municipalities, and many others), French Flanders, Lorraine and Artois, the Balkans, Greece. Other names for the figure include De Sint ('The Saint'), or more formally Sint Nicolaas or Sint Nikolaas; Saint-Nicolas in French; Sankt Nikolaus in German, also known as De Goedheiligman ('The Good Holy Man')

He is one of the sources of the holiday figure of Santa Claus in North America.

Saint Nicholas (Wikipedia)

I think after reading these references, your doubt will be cleared forever :)