trng? i assume you mean a 'truly' random generator.

simply because obtaining random data is very hard (not 100% sure, but i have doubts that something like a TRNG exists). On the level JD is operating on (software on a server), you do not have random input with which your software can work with. OS random generators usually work by taking as inputs various pieces of information (such as time, etc.) and then applying algorithms to them. This results in seemingly random data, however, technically speaking, it is not truly random.

If you want to come closer to pure/true randomness, you would need a special hardware-based generator (for example, one that measures micro turbulances in the air) and base your data off it.

Randomness is a tricky topic