There is a big difference in quality levels. If you want a good mower pay the price for a commercial mower, people who use them 8 hours a day need something that lasts.

30 years ago a friend of mine did the mold for a lawn mower. They put an engine on it and it ran for 120 hours before the deck failed. It took 7 more tries until the deck failed after 80 hours. Commercial mowers are expected to run over 1000 hours.