Many people have found out that in retirement their expenses drop quite a bit. They now have time to shop for bargains, or simply find no need to shop as much. They also discover new ways to entertain themselves less costly.
A lot depends on the amount of discretionary spending in your budget. Hence, before retiring, people spend some effort to track their spending to know what they spend money on. It is so obvious, but I did not know what I had to do. When I first came here to this forum, I was impressed how posters knew more about their finances than I did mine.
You may know and do all the above already. If so, my apology for bringing it up.