There is very little difference between mayonnaise and hollandaise sauce; each is basically an emulsion of egg yolk and fat, with various emulsifiers and flavours added.
The significant difference is that one uses oil that is already liquid at room temperature, and the other uses butter, which must be melted at a higher temperature.
The question is, why can't they be made exactly the same way, but at a temperature that is just high enough to melt the butter, not more than 40°C or 100°F?
I.e. why does hollandaise also require being effectively cooked as well?