Because people are stating facts that just aren't true. The OP wanted a "forever" mower. The battery evangelists came in here with their recommendations. Battery equipment is not at the point where they have earned the "forever" label. Repairability is much better with gas equipment. Parts availability is better, and more shops can work on them. But frankly, the current crop of gas push mowers probably don't meet the "forever" criteria either. Most push mowers have Briggs engines, which, over the past few years, have been cheapened to the point of being a poor shadow of its former self. Briggs has started recommending no oil changes. Just top it off. Great plan to ensure an engine life of no more than 5 yrs. This is why I recommended on page 1,
"If you want a long lasting mower, I'd find a local "flipper". I.e. someone who fixes junk mowers, and resells them. They will know what is reliable and repairable. Personally, if I were buying a push mower now, I'd go with a 3-6 yr old Toro Recycler with Personal Pace. It wouldn't bother me to buy something 10 yrs old if it were in good condition."
I have a 13 yr old Toro with a Briggs flathead engine. I recently moved, and have a larger yard and a riding mower now. I don't really need a push mower any more, but I'm not getting rid of it, because if I ever want one again in the future, I don't want to be stuck with the crap that's on the market now.
I wouldn't buy anything new. And if you buy gas, change the oil every year.