Philosopher of science Stephen Meyer explains in this short Prager U. video why scientists, or at least most of them, have come to believe that our universe had a beginning.
The evidence that accrued between the 1920s and the 1960s pointed to an absolute origin of space, time and matter, and this was significant because prior to the 60s the prevailing view was that the universe was probably infinitely old, and if it were infinitely old it would've had no beginning.
This would fit nicely into a naturalistic worldview, but an origin of space, time and matter, would require an explanation, and the fear among naturalistic scientists was and is that any explanation would sound very much like God.
Meyer explains the evidence that has led to the conclusion that the universe did indeed have a beginning and that the cause of that beginning looks indeed very much like God.
Take a look:
