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I've read and heard multiple times that gravity can't be explained by the current understandings of quantum physics. Wikipedia's Gravity entry briefly explains the incompatibility between general relativity and quantum mechanics on the subject of gravity as follows:

In the decades after the discovery of general relativity, it was realized that general relativity is incompatible with quantum mechanics. It is possible to describe gravity in the framework of quantum field theory like the other fundamental forces, such that the attractive force of gravity arises due to exchange of virtual gravitons, in the same way as the electromagnetic force arises from exchange of virtual photons. This reproduces general relativity in the classical limit. However, this approach fails at short distances of the order of the Planck length, where a more complete theory of quantum gravity (or a new approach to quantum mechanics) is required.

Photons, as I understand, are the force carriers of the electromagnetic field which 'transfer' quantized 'bulks' of energy and, as far as I know, they are not needed for a negative particle (let's say an electron) and a positive particle (let's say a positron) to attract.

So, if two positively and negatively charged particles can experience attraction without the need of photons in the process, why are gravitons (or another explanation) needed for gravitational attraction to exist between two masses?

Edit: I'll explain why my question is not a duplicate. These other questions have good, related answers which I actually learned a lot from. I understand that just as the other fundamental forces have force carrier particles described by QM, gravity still has to be explained in the quantum level. However this is specifically what I don't get (and I could be totally wrong): Photons, as I've understood, do not play a role in the attraction between oppositely charged particles. They have other functions like the transfer of energy. So, why does gravitational attraction between two masses need to be explained by the exchange of gravitons?

Gabe12
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If a universe has any quantization of energy at all (as our universe does), then everything must be quantized and nothing continuous. Otherwise, if there are both quantized and continuous forms of energy, where is the extra energy stored as it moves from one form to the other? If we have quantized energy flowing into a continuous form, then it must either flow continuously out of the quantized form (and therefore that isn't quantized), or enter the continuous form as a packet (and therefore is quantized). If energy moves from a continuous form to a quantized form, then it must be temporarily stored somewhere as it builds up enough to be moved as a packet to the quantized form--and where is it stored? Energy can certainly be held in a gravitational system, therefore it must be quantized, and that's a graviton.

Digiproc
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