the easiest way to answer that is the older garden tractors that people used for lawn mowers were all built heavier - lawn tractors are much cheaper, you used to be able to buy a craftsman/wards/gibson/ford/wheel horse/cub etc.... and they were 95% built for stout and going to last a LONG time = 20yrs if you took care of them, now you will likely get a 5 yr mower if you take care of it, many of the various bushings are metal on metal or plastic inserts - you have to spend $$$ to get better and know what you are looking at - very few are able to be lubed - steering gears cheap or the bushings holding shaft wear/frame etc....just disposable etc.....same as cheap zero turns that use inexpensive hydro motors that dont last - blah blah - even my john deere hydro is cheap, you can buy a replacement for 300bucks and it was a 5000K mower when new - you have to be in the 6 to 8K range to even sniff a descent mower these days and more like 10K if you want all the stuff an older tractor offered.
Example, 1997 Ford GT75 made by shibaura - Japan - they ran 9K back then = power steering, hydraulic lift, dual range hydro, cruise control, tilt wheel, spring loaded seat, 3cyl diesel, drive shaft from engine to hydro, drive shaft to gearbox on deck from engine, honestly they will
View attachment 612155View attachment 612156 last a lifetime - many others like it i just use it because i am familiar as i have owned one - best mower ive ever owned as far as reliability. Built like a stinkn tank but I could barely lift the 60" deck and wrestle it out from under the tractor, it was a beast truly.
you will have to search long/hard to find tractor style mowers these days like the older deere/cub/wheel horse/ford etc....and pay a premium for them most have been replaced by SCUT these days - riding mowers are mainly made disposable nowdays like washing machines/dryers/refrigerators etc......