The 'halcyon days' of the sidelever preceded widespread use of ejectors. I have three sidelevers - an 1894 Grant SLE, an 1886 SLNE Boss and an 1888 BLNE Powell - all with
'right hand' levers. The Grant is a 'pain' if you're trying to block hulls from being ejected.
For me, levers on the left (I've used a few) are much more 'ergonomic' on extractor guns.