Small frames have steep seat tubes for a simple reason. It is not because anyone imagines that small riders pedal differently. It is about keeping feet out of the front wheel. Steep seat tube brings the bottom bracket rearwards. Shallow seat tube sends the bottom bracket forwards.

There are only three things a designer can do to move the front wheel away from a riders feet. One, longer top tube. Obviously there is a limit on that for smaller riders. Two, increase fork rake. Building different size frames with different fork rakes is relatively expensive. Manufacturers don't do expensive. Using enough rake to make a difference is beyond the imagination of most. Few if any have any understanding of rake, trail, handling. Number three is adjusting the spread between seat and head angle. If the seat is steep and the head shallow small frames can have toe clearance. Even on big frames if you stray far from norms there will be lack of clearance. The limiting factors are the bike handles poorly with very shallow head angle (especially so if the rake is not adjusted), and the bike can't be pedalled by most normal humans if the seat tube is too steep.

The spread of plausible seat angles for road bikes is very narrow. 72 to 74 degrees is about it. 75 degrees for small frames. Fairly straightforward. There are jokers in the deck. Time triallists and triathletes (not normal people at all) use different angles and then create a fashion thing that gets applied to normal bikes for normal people. Nut jobs like yours truly are perfectly happy riding DL-1s with 66 degree seat angle and the seat clamp in 'normal' position. DL-1 is a good data point for what happens with shallow angles. The wheelbase is 47". This has some purpose, the bike is wildly stable. But most do not want a bike that long and they don't want a long bike with a 68 or 70 degree seat angle either.