^ A bit of deposits on the intake manifold past the throttle body are not a problem unless it's fouling a sensor or some other (idle control perhaps) valve. On the cylinder intake valves if it's not direct injection you have the fuel injectors (or carb going back decades ago) external to them, cleaning them off and reducing buildup rate due to running cooler from the flow of fuel past them. You might have to clean your throttle body too once on a blue moon but it's not the only source of deposits, you still have EGR.
If you have some bolt on (external) sensor or valve, it can be cleaned later or replaced more easily and inexpensively than adding a catch can and monitoring, emptying it periodically. It could also result that on some engines a catch can is going to reduce crankcase vapor scavenging (which keeps oil cleaner) rate so for equal protection your oil change interval may need to decrease. That can also cause higher crankcase pressure which reduces engine efficiency. Engine tune and piston rings can expect a certain PCV flow rate and crankcase pressure range.
In other words, of things people bolt onto engines, there just hasn't been significant enough benefit for a non-DI engine and some drawbacks. Consider those who design the engines, granted their designs cause a problem on DI but the non-DI engine has been around for a long time.
If the catch can had a cost effective benefit it would be on the engine already. If it were even the best solution for DI engines the manufacturers wouldn't be looking at ways to add an additional external injector instead of a catch can.
