OHC engines almost always are designed to rev higher then pushrod engines.
Higher revs will result in more heat energy, and greater wear on parts. This could be designed out by increasing surface areas of bearing surfaces, increasing lubricant flow, improving the cooling system, along with some materials changes. You will also need a mechanism to drive the head cam, which is also subject to design requirements.
You are also more likely to look at having more valves per cylinder to aid the engine revving. Whilst you are doing that you will also probably increase compression ratios, which in turn requires a closer examination of how to secure the head from escaping higher pressure gases.
You will then have a trade off over the physical size of parts, and on a bike that will be important.
There is also the trade off of costs.
A push rod engine will usually be cheaper to manufacture.
All the above being said, engine design has moved on dramatically since the '70’s where top ends of engines were often the limiting factor in the life of a motor cycle.
These days bikes can expect realistically to go well over 100k miles without a top end rebuild - and you could not have really said that 40 years ago.