This forum is for TTN so it’s a bit much to expect us to recommend another service but you may want to look at Chirpstack.
As for the why, perhaps you need to direct your question to Dragino.
OK, thank you. Don’t worry, I could not be your customer anyways because of current hardware, but will get back when I got compatible by remembering good deeds 
FYI, you can’t be a customer - TTN is a free service and we are volunteers.
But you are more than welcome when you have an 8 channel gateway.
As Nick says you need to ask Dragino for full answer but suspect in large part it is the typical practice within the industry of having common core firmware/software across a number of devices & families - even if ‘options’ do not always reflect actual device capabilities or system implementations. You can use this in your own private deployments, where limited functionality may be adequate and you do not impact other users.
For anyone else reading at a later date this is classic ‘Caveat Emptor’, and why we strongly recommend researching and reading around the subject before diving in and buying kit…here the TTN Forum is your friend (use search) as there have been lots of posts about suitabiity of equipment over the years, and many Forumites more than willing to share their experiences and opinions of targeted hardware or to make suggestions based on declared needs. Also make sure you read full, and current, information from potential vendors and if clarification needed ask them or ask on the Forum - Forumites dont always pull their punches and if we think something is not suitable or a poor choice likely you will hear it 