The Belgian, 31, joined Club Brugge last summer after six years at Anfield.
"I sat on the bench for about a year-and-a-half," Mignolet told the Mirror. "At 31, you're in the prime of your career as a goalkeeper, so you want to be playing regularly.
"If I was going to sit on the bench for two more years, I would have been 33. Alisson is such a great keeper, even though I knew he might get injured or suspended.
"So maybe I'd play five, 10, 15 games a year, but to then try to find a club at 33 and be a regular starter is difficult, so I took the chance to do it now.
"Although I was very happy to end my time at Liverpool by winning the Champions League, you always want to have more of a bigger hand in winning trophies.
"It's so much nicer to feel a victory when you've been on the pitch, when you're contributing on a weekly basis, which is what I do now."