In a less "everyone is s**" take than siblings, this could be a number of biases:

- Availability/survival bias: People took fewer pictures in the past and were more likely to be taking those pictures on special occasions (when they were dressed nicely).

- Now that we live in a world of generational fashion, the previous generation's "casual" wear becomes the next generation's "dressy" (read: stodgy) wear.

- People owned less clothing, had less access to varied clothing, and laundry processes were harsh, so they wore sturdier (and heavier) clothing that more easily supported "dressing well".

- "Back in my day, people conformed" isn't exactly a novel take.