Is it compulsory for IGNOU students to visit study centers regularly?

It is not required at all.

You need to go to the study center to get your books (which are also available at regional centers), submit assignments (which are mandatory), fill out your examination form (which can also be done at regional centers), and attend practical classes (if you have any practical subjects).

In some cases, regular classes are held at the centers for specific courses. They are attended by some of my friends. However, because it is an open university, it is entirely up to you whether or not to attend them.