Availability and cost are probably some of the main reasons. No need to design and manufacture when you can just buy it without hurdle.
Is it any more available than any other drone maker though?
Are there design features that make it more adaptable to kamikaze use?
Did Mugin happen to have a successful RU/UKR sales rep and so they are using what they are familiar with?
Like we see so many videos of DJI Mavic being used by both sides, but obviously DJI is number one and Mavic is their best seller, so it's not really surprising. As an aside, DJI manufacturing is crazy impressive. You see the Russians and Ukrainian forces with actual pallets full of drones, and still DJI can manage regular retail sales (Mavic mini on sale at Costco!)