Is there any reason not to use std::make_shared when constructing objects?

Answer 1

If you are constructing an object that will have multiple entities sharing in the lifetime of the object, then yes, you want to prefer to use std::make_shared where possible. Some places it might not be possible is if you obtain the pointer from someone else; for example, a factory might return a raw pointer or a std::unique_ptr that you would like to store in a shared_ptr, thus preventing use of make_shared.

The question in the title is a bit different; there are plenty of reasons you might not want to use shared_ptr for your objects at all. You should only use shared_ptr if the lifetime is actually shared by multiple objects. Otherwise, prefer stack allocating the object or using unique_ptr.