In 40 years of riding, street and dirt, cross country trips, etc, I have been stranded ONCE.
That was a few years ago on a 1969 Triumph Daytona.
The aftermarket tappet adjusters I used (mushroom head) started chipping their edges off, which got into the oil pump and trashed it.
Oil pumped into the motor, but not out.
That after 45,000 miles of hard riding it.
True, it always needed work, but I used the bike hard.
I almost did not make it home a few times, an old IT175 sucked in a reed valve on the trail. I used a soda can to replace the missing assembly and rode home on the other reed.
In the 70's, I burnt a hole through the top of the right side piston on another Daytona, I sort of did it because I got fed up with it slowing down at full throttle.
I made it home on the left cylinder.
Most bikes can be very reliable if you look after them.
Most breakdowns are the owners fault in my book, cables, carbs, chains, wires and connections are things that need looking after, batteries should be replaced before they get old.
Modern bikes can have fuel pumps, which should be replaced at some point.
Every component on a bike has some expected lifetime, you just need to know about what it is and replace it beforehand, or carry a spare.
Points, fuel pumps, carb parts, cdi units, throttle position sensors, you think about what could kill your bike and plan for it.
A new bike will have nothing to worry about in most cases, except some Euro brands with a lot of electronics, an old bike will have almost every part suspect.
There is no reason an old bike can not be as or more reliable then it was when new, if you go through it.