The only true incentive for reporting a bug is having it remedied. If ESO offered some sort of other reward, they would be swamped with reports of bugs that don't exist. They'd probably agree if I said that they have enough of those already.

In my own professional experience, first, what a user regards as a "bug" is not necessarily a flaw in the operation of the software. It might be an oversight or defect in its design, particularly in the features of the User Interface, which is a different problem. In many cases, the event which occurs has its root cause in the user's computer system and/or local area network (or even in the user's ISP network, and sometimes in some malfunction in the Internet itself).

Second, no one can find and fix what does not exist. Which means that a programmer must be able to cause the "bug" to become evident. To do that, a programmer needs a clear and complete description of the exact circumstances and the user's actions which resulted in the malfunction, and a description of the outcome such as erroneous output. If the game software and/or the user's system displays an error message, then the exact message (or some way to identify it, such as an error number) should be included in the user's report, and one or more screenshots can be helpful.

Quite often, information reported by the user is simply insufficient to enable a programmer to reproduce the "bug". To be fair to the user, it can be difficult to discern just which information a programmer must have to reproduce a "bug" and to investigate its cause.

Third, when a programmer cannot reproduce the "bug", it is usually impossible to find the problem and remedy it. This is true even for output which a programmer recognizes is flawed, such as a value that the software is not calculating correctly. The programmers who investigate "bugs" have to be really good at solving puzzles. Unfortunately, too many of them are good at writing "puzzle code" instead.

My two cents.