Aluminium alloy has a very low fatigue life.
Thus even if the engine was used exactly according to the manual and service better than by the book there is a finite number of timed the rod can go back & forth till it goes bang and that is regardless of what it is fitted to.
Vertical shaft mowers are built to a cost, the cheaper the better, because they buying public is mechanically ignorant, economically ignorant and cheap.
Add to that modern design & testing tools then you can engineer engines that all will fail between 500 & 550 hours.
That is about 10 years.
The Ford mentality is very strong ( made just good enough to outlast warranty ) and Ryobi has become the master of this.
Jo public buys a tool and it works reliably and well for 5 to 10 years then goes bang and you will happily go back to the store & buy another one.
If you want to know the mechanism of failure then you will need to post some better photos with clearer focus ( phone cameras are not good enough ) and close up on all of the fracture surfaces.
As for all you zoom heads, it died because 2 stroke oils get a lot better and in particular became self dispersing.
Profit margins at service stations has not changed in real terms for decades.
When real petrol was 3 shillings a gallon we were making a 6 p profit on it. (about 15%)
Now it is $ 5 / gallon and we are making 30� gross profit (about 5 %)
The greedy selfish buying public decided that saving lolly bar each week on their fuel bill was better value than having their vehicle properly looked after and providing entry level employment to some one else's children.
