Helicopter pilot reported while in the VFR pattern observing an private jet entering the runway without transmitting on the CTAF resulting in an aircraft on final executing a go-around to avoid the private jet.

Narrative

Private Jet (PJ) type aircraft entered Runway 27 for departure without SA (Situational Awareness) of two aircraft on final; causing one go-around.I do not recall the type/model/carrier; but the PJ was at the hold short for Runway 27 while multiple aircraft were working the traffic pattern. Two aircraft were in line behind the PJ on Taxiway A; and after some time of the PJ holding short; one of the smaller GA aircraft asked the PJ by tail number if they were departing soon; otherwise they would take an earlier runway entrance to depart. The PJ did not respond (this is a common occurrence at JZI because the air crew is frequently on the departure/clearance frequencies obtaining their IFR release). After some time; the PJ finally came up on the frequency as they began taxi on the active runway and stated they were departing Runway 27. The aircraft on final declared a go-around and a right-hand offset of the runway; and the PJ took off from the runway without stating anything. The second aircraft on final was able to continue and make a safe landing. All other aircraft in the pattern and on the taxiway were making appropriate radio calls IAW (In Accordance With) the AIM (Aeronautical Information Manual).I have observed a significant increase in instances such as these as the commercial operations at the field have increased. As much as that mishap frustrated us in the pattern with my first reaction being anger towards the PJ air crew; I am also aware that mistakes happen. There are often mitigators which can prevent the worst from happening which account for some of these common errors. Over the last few years; the concentration of traffic at the airport has become consistent with that of a towered/Class D airport and I think it may be time for that.