Html5 vs SAP UI5

Dear All,

SAP UI5 is pretty new but the technology has grown at a high pace.

My question is what are the reasons that still the development are done in HTML5 .

Bottom-line being,  where does HTML5 still has an upper hand than SAP UI5.

And where are the things still to be enhanced in UI5 technology especiaaly when we speak for standard desktop application.

Regards,

Puja