Orks are at a real sweet spot, both crunch-wise and fluff-wise. They have slightly lower maximums to some Attributes, but not enough to be a huge hindrance, while getting bonuses that put them right about where most characters want to be. A Body of 4 and Strength of 3 are good for even a non-combat character. Overall, they gain 20 build points compared to a human (20 cost and lose a point of Edge, vs. 50 points of Attribute bonuses). Fluff-wise, they are a relatively common metatype, suffer moderate discrimination, and can generally blend in relatively easily, not needing customized gear, or living spaces designed for a different size.
Dwarves, by contrast, cost 25 points, lose a point of Edge, and gain 40 points in Attributes, for a net gain of only 5 points - not really enough to balance the hit they take on Reaction and the requirement of gear modified to their size.
Trolls cost 40 points, lose a point of Edge, and gain 80 points in Attributes. So their net gain in build points is even more than an ork's, but Body and Strength of 5 are getting to the point where they are too much for a non-combat build. And they also are huge sized, need specially modified gear, and take hits to their maximums in Agility (one of the most important Attributes of the game) and mental Attributes - unlike an ork, the latter are enough to be a serious detriment in certain roles (face, techie, etc.). They are great for certain builds, but handicapped outside of those narrow roles. I admit, though, that I still like playing against type with trolls (stealthy faces, etc.), even though it is not very optimal.
Elves cost 30 points, lose a point of Edge, and gain 30 points in Attributes. They are the only metatype that actually has a higher net cost than being a human. But what you are paying for is the ability to have two very important Attributes at a higher rating (or, if you don't get a high Agility or Charisma, you are paying a "flavor tax" - the weapons specialist archetype is an example of this).
Humans, the baseline, are very versatile. But their biggest weakness is that they are the only metatype without some kind of Attribute bonus. Which means they are stuck with 200 points in Attributes, while, for example, an elf could, in effect, get 230 points worth of Attributes. This can limit humans for some roles, ones where above average physical and mental Attributes are needed.