in order for the dropping point of a grease to be important the global temperature needs to be high, and as you say in most bicycle applications it isn't. However that doesn't mean that additives that 'work' at high temperatures are wasted in a lubricant that sees low global temperatures; far from it! You should not conflate the presence of things like MoS2 in a grease with that grease being specifically designed to work at high global temperatures only; the grease may well be designed to operate at high pressures and that alone is sufficient to justify its inclusion.
The reason is that whenever there are high pressures there are also high temperatures; it is just that these may be very localised and also transient. However they are high enough and they last long enough that all kinds of EP additives and solid lubricants have a chance to work in the way in which they are intended to, despite the low average temperatures.
For example if there is a particle of steel that is 'run over' by a ball, and crushed, it will reach temperatures of several hundred degrees and unless protected in some way there will be galling and welding between the surfaces. Chemical EP additives help but are not a complete solution; this exact mechanism is one that causes a lot of wear.
And local pressures are very high in bicycle bearings; they are moving very slowly (vs similar bearings etc in most industrial machines) so the metal surfaces are not separated by a film of lubricant as is found in full hydrodynamic lubrication. At best you get a mixed mode in most bicycle applications, and more often than that it is a boundary condition that applies; exactly the conditions that are most mitigated by having solid lubricants of various kinds in the grease.
As I explained (at some length) earlier some lubricants that work well at low speeds don't work well at very high speeds (speeds that are not seen in bicycles), such that rolling element bearings may not roll but can start to scuff instead, which causes all kinds of problems. Or the work rate in the grease is so high that it overheats, just from the viscosity of the solid lubricants in the oil, leave alone the effect of any thickeners. So greases that are designed to work well at low speeds only
are not to be easily found in (say) a car spares shop; the applications for them don't exist in most modern cars. The greases that you will find easily that work OK at low speeds are usually ones with limited MoS2 content; just enough to make them work OK in CV joints etc (but they are far from the best greases for this) but not so much that they won't work in higher speed bearings. Otherwise you would get idiots putting high solids greases (for low speed applications only) into wheel bearings, which can cause the stub axles to shear at motorway speeds....
Arguably the closest thing you will find to a proper low speed lube is something like a MoS2 assembly paste, which can contain up to ~50% MoS2; probably this would be pretty good in bicycle bearings....
The other thing is cost; solid lubricants need to be manufactured and graded into particles of controlled size before they are added to lubricants; this can be expensive. Lubricant manufacturers don't bother making lubricants that are more than good enough for a given application; 'just good enough' is 'plenty good enough' in their book, and in most cases they are more fixated on lower running drag (i.e. lower friction through viscous losses) whilst retaining adequate life than they are in creating a lubricant that will completely eliminate wear per se.
Similar concerns exist in bicycles; for example if you run hub bearings in oil, there may be lower drag whilst the wear rate is low enough that the service life is acceptable. Or the wear debris gets flushed out by a 'total loss' regime, in which oil comes out of the bearing in service (carrying the wear debris with it) and needs to be renewed on a regular basis; this is how most bicycle bearings worked for about the first hundred years of there being bicycles with rolling element bearings in them. Ditto running bearings without full contact seals. These things may 'cost' less than 1W but when you are racing every little helps, or so it is believed.
[Witness those that spend a fortune on 'ceramic bearings' because 'they are faster'. Well the main 'benefit' of using them (which is actually tiny anyway BTW) comes from the thinner lubricant that can be used in them, whilst retaining an adequate service life: If the bearings were better designed in the first place, they would tolerate being run in oil for a race distance anyway; no need for ceramic bearings.... this is how Hinault's race mechanic prepped TT bikes BITD...]
if you choose your lubricant carefully, you can get extremely low wear rates in all kinds of bicycle components, such that their service lives are practically infinite in wear terms; the parts are then likely to fail by fatigue, eventually. However because of the low speeds and high pressures seen in bicycle bearings, solid lubricants are, I think, a vital ingredient in the best bicycle lubricants.