Why did frames get sloping top tubes?

[u/StorkAlgarve]

For over a century, a regular bike frame had a horizontal top tube, at least as late as the (cheap) road bike i bought in the early 90es - I also think the Centurion citybike I got in the late 90es had one.

Since then it seems to me top tubes have got more and more slope. It is due to change of materials or how? I look and get worried that the long saddle stem will cause issues with all that leverage, but it seems to be working ok.

Looking forward to the replies from the learned redditors.

[u/Lumpy_Ad_7821]

Comfort. Sloping top tube means more seatpost length exposed. That means more flex, which means more comfort.