DICOM supports MP4 (and HVEC/H.265, various flavors of JPG, and various other encoders, etc). I don't think PNG is supported, though and I'm not entire certain why but possibly it's a licensing issue. DICOM objects are basically just generic containers.
There’s probably multiple reasons why DICOM does not support PNG. Most compression formats in DICOM are those published as official standards in the JPEG family from ISO.
The original JPEG from ‘92 already included a Lossless mode which supports 16/12/8 bit color and monochrome and is very fast to encode and decode. All of those were important features.
Adding PNG later would not benefit anyone: it can not handle all of these usecases, it is usually slower and it came later.
