Why Are Most Apps Available For Iphone And Ipad But Not Mac Computer Desktops

I have a brand new Mac desktop I bought in August of this year and I would like some of these apps. Would they work on my iMac or not. If not, why don’t they make these apps for the iMac to?

For example Ugly Meter and Am I Ugly are 2 apps I would love to try, but they say they are good for iPhone and iPad. What about making them for iMac to?

Please answer this question since it has been bothering me for a long time.