Because we are not going to add hundreds of parameters from hundreds of others filters to cover every requested combination (this is not the only suggestion like “every filler should have ____”). This is the reason Filter Set was created. In fact there is already a stock one very similar to this called Obscure With Mosaic.
Smooth-Filter which creates Inter-Frames like ffmpeg’s “minterpolate”
It is too slow to do in realtime especially when Shotcut is already as slow as it is. Something like this should only be attempted when hardware decoding is integrated with a GPU effects pipeline. In the meantime, you should use Properties > Convert > Advanced to increase the frame rate with interpolation.