In the last 50 years both rifles have evolved. There were good and bad years as well as good and bad examples of both the Ruger and the Marlin. If you've owned several examples of both over that 50 year time period I think it is easier to understand that. If you've only had a limited exposure to one of each it would be easy to come to very different conclusions.
If you compare the Marlin to the standard Ruger Carbine, Marlin wins on ergonomics. The standard Ruger stock design is poor. But the Ruger Sporter stock is the better of the 2 in my experience. The cost difference is negligible and I've never understood why those aren't more popular.
The Marlins tend to be slightly more accurate and have better triggers out of the box. But that is true 100% of the time. And it is a lot easier to correct a bad Ruger trigger.
Ruger wins on scope mounting.
In my experience Ruger wins on reliability and durability by a wide margin. The weak link on the Marlin is the tube magazine. You can only pull that tube out and load it so many times before it wears out. Granted, for a lot of people that is a lifetime of service. But not for others.
My Marlin was bought in 1968 or 69. The magazine started failing at least 20 years ago. It is no longer usable, and not worth the cost to repair. I have worn out a couple of the Ruger magazines too. But they are easy enough to toss in the trash and just buy a new one. And like most people I have multiple magazines. I actually prefer the 10 or 15 round mags that protrude slightly from the rifle. It isn't enough to get in the way, and they are a lot easier to remove and insert.
RUGER RUGER® 10/22® 15RD MAGAZINE 22 LR | Brownells
Butler Creek Hot Lips .22LR 10/22 10-Round Magazine (gunmagwarehouse.com)
The Ruger Sporters and target versions are plenty accurate from the factory. The Ruger BX trigger comes from the factory on some and is available to put in any of them. That will give you a 2 lb trigger that is better than most any other factory 22 trigger.
The Ruger wins on aftermarket accessories. With the ability for anyone to swap out barrels and virtually any other part easily with no gunsmithing you can create anything you want and outshoot any Marlin.
But that does cost money and not everyone wants to do that. That is why I think there is room for Ruger to make both designs.