MediaTek has long been known for making inexpensive chips for budget devices. I think they're trying to break into the premium device market, but they're still mostly in cheap phones and tablets. Cheap equals low capability.
Because mediatek company from china.
In chip industry huge number of technologies which can be used as a military.
Some technologies can't be licences to some countries or licences is limited.
GPU good for fast concurrent calculation. Such type of calculations can be used for product for military.
It's just one part of answer.
Such situation with companies from Russia. They have some limitation for using new CPU and chip technologies.
Also such countries can't buy some manufacturing devices.
It's company from china.
Some technologies can't be shared with china and other countries. For example Russia also have some limitation.
GPU is good for concurrent calculations. Such type of calculations can be used by devices for military.
If china want to manufacture fast GPU they must develop such GPU from scratch.
China also have limits of their technologies for export. Such limitation is usual for new technologies in different spheres.