A mosque is a center of worship, congregational prayer, recitation, learning, and mutual care. أَحَبُّ الْبِلَادِ إِلَى اللَّهِ مَسَاجِدُهَا highlights this religious significance. Respect includes cleanliness and consideration for others worshipping there.
Pushing past others, interrupting their worship with unnecessary noise, or neglecting cleanliness conflicts with that respect. Love for a sacred place should be visible in conduct.
مَسَاجِد is the broken plural of مَسْجِد, related to the root س ج د, “to prostrate.”