Why Hotspot Shield?
Flexx Defender of the month mod
Well, that totally depends on the developers, what they feel like is good for their product.
Even kaspersky uses the vpn engine of Hotspot Shield in its products. So, if many known anti malware manufacturers are using the engine of Hotspot Shield in their vpn product, then there might be something good about Hotspot Shield that makes it better and different from other vpn vendors.
Hotspot Shield, has been there for a long time in the market, released in 2008 whereas NordVPN was released in 2012. Nevertheless, even NordVPN has also become one of the most used vpn service in the world.
While this is not the matter of issue but as told earlier it is totally upto developers as to what they feel like is better for their products. They are the developers of the software, they tend to know more than us as to how things work, which product will be compatible with their product etc. There is nothing that can be done in this case from our side.
OMEN Laptop 15-en1037AX (Bitdefender Total Security) & Samsung Galaxy S22 Ultra (Bitdefender Mobile Security)3
@mrmirakhur is right, as a trusted provider, when choosing a partner, there are several things to consider, such as their reputation, reliability, ease of use for the consumer, compatibility with the existing portfolio, technical limitations, cost effectiveness, available support resources and long term development. So it's really up to the developers and their expertise to choose what is best suited for the products.