Why don't more lever guns eject from the side instead of the top

[Tommygunn]

Well, even some of the really early Marlins had side eject so it wasn't a metallurgical problem it was design. I don't think most lever rifle makers back then really thought about scoping their guns. Even Marlin was thinking more of keeping the ejecting brass from obturating the sight picture. Winchester didn't think that was important since it only lasted for a fraction of a second.
Most scopes back then were loooooooooonnng brass tubes that pretty much ran the length of the barrel plus the receiver....and most people who wanted them wanted heavy hitters like the Sharps and Remington Rolling Blocks 'cause they wanted the BIG game like buffalo.

 

[vaupet]

First, the toggle link design wouldnt alloy for a side port,
Second, the open top makes hand feeding that next cartridge very easy, comparable to the falling block rifles

 

[vette20]

I am left handed and prefer lever action rifles with side eject. I own a Marlin 30-30. Last week i purchased a Browning BLR lever action in .270. I wasnt aware until recently that Browning made these in almost every calibre. This is a great gun and is clip fed which allows you to use almost any type of bullet.