In case of UE specific data transmission MAC layer allocates radio resources on dynamic basis. When we say dynamic resource allocation it means in each TTI (subframe) different amount of data is sent over the over considering various factor QCI, amount of data buffered at RLC and available radio resource.
What about the MBMS data transmission. MBSFN subrames are fixed in radio frame for the MBMS data transmission. Is there really need of any dynamic resources allocation for the MBMS data comes from RLC layer or it is persistent since required modulation and coding other parameters are already known at the time of bearer establishment and these parameters does not change throughout the data transmission of MBMS data.