I still see 20+ year old 4 strokes on the water, so that arguement is moot. Seen a pontoon recently with a first gen yamaha F9.9. I think late 1980's.
same deal with an old 2 stroke. When it overheats (and a lot of them don't have overheat protection), it's junk, can't get parts for them so you throw it out and buy another. Most 4 strokes have overheat protection; limits RPM to like 2500, so you can limp back. It's there to remind you that it's hot, shut it down. Unfortunately many don't, they just keep going, "why's this thing running like poo????" Seen it on 2 stroke and 4, more often on 2 stroke stuff though and may be because there are more of them around.
4 stroke powerhead can be rebuilt, easily. 2 stroke powerhead can be rebuilt easily too, in both cases so long as the parts are available and the owner is willing to put the money into it. Did a 25ESH last year, $1400. Did an F20 earlier this year, $1280. There isn't a big price difference. Once you get into bigger stuff that changes. Dual overhead cam, etc. But compare that to a FICHT motor, or a HPDI, and the costs are roughly the same. You can get reman powerheads for 2 stroke and 4 stroke both (aftermarket) and OE supplies new powerheads for both as well. I haven't priced them. Not that it matters for anyone but those who use their stuff offshore for many hours a day, or duck hunters who haul their stuff down dirt roads for miles and miles, fills the underside of the cowl with dirt/dust and there ain't no air filter on outboards (ain't much dust on the water). That is considered unusual operation. #1 cause of powerhead failure is dirt dobbers. The little buggers build nests under the cowling and all over the engine. Owner gets his stuff out of year of storage, fires it up and takes off. Those nests break loose and get pulled into the engine. Dirt is not a good lubricant, fuel, or coolant, so the engine loses compression. Seen a few dozen of those. That is considered neglect and it don't matter if it's 2 stroke or 4, they're both gonna suffer the same fate.
the reason you see 60+ year old outboards is because outboards and boats SIT without use. Some more than others. Dad don't use his but once or twice a year now. I use mine every single weekend. My friends (retired) use theirs daily, couple hours of use a day usually. Stuff wears out with use. If there are a million motors sold and 500,000 of them get used once a year, then half of them are likely to be alive for a long time, but you don't hear about the other half that were worn out, dusted, neglected, abused, totaled, sunk, etc.
