Midi note Velocity doesn't follow dynamic changes

I transcribed a piece for violin and piano and inserted dynamic marks in both staves . when I exported the midi files of both instruments, the piano notes showed variation in velocity but not the violin. I checked the violin track in play mode (of Dorico) and can confirm that the velocities have the same constant value throughout the piece. The only thing that changes is cc11 (the expression track) .
I wanted to import the midi files into Cubase (to be played by a VST synth) but I then had to manually adjust all the note velocities.
PS: while on the subject of dynamics, if I want to add a dynamic mark on a piano score, do I have to add it to both staves or just the treble clef?
Dorico 3.5 elements/ Cubase 10.5

This seems to be normal. Like a drum, a piano strikes its strings once each time a note is played no matter how long the note is held, but a violin can increase or decrease its volume during a long held note. Therefore, a violin should handle volume control via different means. For a violin, velocity might well be used to control the speed and strength of the attack on a note, but not its volume.

When you add dynamics to a piano instrument in Dorico, add the dynamic to the right-hand staff: Dorico will correctly centre it between the two staves, and it will take effect for both hands during playback.

Thanks’ for the reply, That makes sense.
Now I’ll just have to work out how to get my synth plugin to respond to expression data.Cheers