This has to do mostly with wood choices.  

Typically the weight is between 8.5 pounds (3.85kg) and 9.5 pounds (4.3kg).

For reference the average electric bass guitar is usually in the 8-12 pound range.

That is to say, that Megatars are not unusually heavy. 

The included strap is quite comfortable, doing a great job of stabilizing the instrument in the proper playing position and distributing the weight around your body.  Customized 3" glove leather straps are available as an upgrade and are highly recommended.  

If weight is a primary concern of yours, an ultra-light model can be put together with appropriate woods, hardware and electronics choices.  Inquire.

Attachment points can also be built into a Megatar to allow the use of 'lap bars', 'belt hooks' and other forms of support.  Inquire.