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@Faux Science Slayer

There have been birds just in the past 10M years with far bigger wingspan than a condor - that does not imply massive climactic differences.

In many cases size of animals is not limited by simple "single factor" scenarios as a whole host of competing costs and benefits kick in.

e.g. the condor can fly very well, not expending too much energy and cover large distances at a good speed (ideal for carrion searching) - increasing wingspan a lot would only give relatively small increase in speed / range but would come at the cost of higher food requirements, body more effort to move on ground /more awkward to take off (i.e. harder to escape ground based predators).

With higher food requirementrs would there be enough carrion (remember it has to compete with other carrion eaters & finite rate of dying animals as not an active hunter)

Greater size could make the bird less "agile" in manouvering in the air (remember condor is not 100% immune from aerial predators, if it was far larger & clumsier a smaller eagle / hawk might be more likely to risk attacking it )

Even basic things like nesting sites may be more problematic with increased size past a certain point.

Condors could be larger (they have not reached a mechanical / cardio vascular size limit), but for whatever combination of reasons, there is insufficient advantage in doing so.

Ecosystems are complex (though people are doing a good job of making many of them simpler by heavily reducing / wiping species out) and it is too easy to make rash assumptions.

The occasional one can be valid, e.g. in times of higher average temperaure and oxygen levels then insects could exceed maximum possible sizes we see now as the passive spiracle based "breathing" system of insects limits their size due to limits on )2 delivery over distance and so higher O2 and tempearature would facilitate larger insects as more O2 and higher temps increase gas speed. But in general size X must mean physical factor Y are wrong.