Why don't they make them of aluminium, then it'd be a job for life suppose they'd not sell enough lawnmowers then.
I have a brand new mountfield sitting in the garage, haven't had it on the lawn yet and just know as soon as its used the decay will start, have to make sure I clean it properly and use some sort of rust inhibitor on it over the winter. I have had only 2 petrol lawnmowers over the last 24 years, normal self propelled jobs, 1st was well patched and welded then the engine seized. Bought a new one which must be 10+ years old now, also patched and repaired but still going strong
in a nutshell, not in their interest to make them long lasting. There's money in the spares market. I'd think it would be fair to say that the majority of lawn tractors are scrapped due to the deck being shot, more so than the rest being worn out.