ITBS need general maintenance with balancing and cleaning once every few months really depending how much it's used. Sharky had a run of bad luck but the engine in his trophy was rough to start with. Which was overlooked by there tuner. I just like going through engines.
The lump that did a head gasket on mine recently was a scrap yard engine with some cams thrown in to boot. It's no basis to base your own purchase on lol.
ALL engines will ultimately die, it will just happen quicker if they are thrashed, and by definition if you are fitting a set of bodies its because you want to thrash the engine, otherwise there would be no point having them.
So its partly about the use that an ITB car will typically get.
Same story with a turbo really, look at the engine in my old car, it was a high miles snotty old engine to begin with, MWM then turbo'd it and Jack from MWM drove it around for a few thousand miles with no issues, then Aydon bought it and drove it around for another few thousands miles with no issues either (but all road use no trackdays). Then I bought it and started doing trackdays with it every chance I got and increased the boost and just generally gave it a much harder life, and it relatively quickly expired after that.
These engines are all 10 or so years old now, and essentially over halfway through their lives anyway in a lot of cases.
Put it this way, if you were going to put together a new rugby team, would you go and get healthy young lads from the local college or would you go and pick your squad from the old folks home? lol