Blood Alpha Sam Cooper explained this in Chapter 4, but I wanted to list them here with details in case you need to return to it later.

Mahani are rejected for five main reasons: 

1 - Fated mates will NEVER be the same rank as a Mahani. 

This pairing is frowned upon in most packs. Some that follow the old ways even have laws against it. If you read the chapter on Ranks, you will understand this better. 

2 - Mahani shifts do not look like pack wolves. 

They look cute and cuddly, like an oversized dog. While all wolves must shift regularly or become uncomfortable, the Mahani will usually not shift publicly unless necessary. When they shift, it makes them readily identifiable as a Mahani. It has all its powers in human form and wolf form.

Shift sizes are as follows:

Alpha and Betas are the size of a normal Delta/Gamma Pack wolf.

Delta and Gammas are the size of an Omega Pack wolf.

Omegas are the size of a large dog breed.

Elementals are the size of a puppy.  Their transformation is the size of a large dog breed, the same as the Omegas above.

Blood Alphas are the size of a normal Alpha/Beta Pack wolf unless it is an Elemental.

3 - Mahani do not live in packs; they have tribes. 

They do not own pack land and live primarily in Lone wolf communities or within small human towns. For this reason, the Mahani will go to live with their mate unless the situation is abusive because Pack wolves need to be in a pack, so most do not do well within the tribes unless they have an aversion to packs. The look of the Mahani's shift may be very uncomfortable for the pack and the destined mate. Wolves are prideful creatures, so this is a huge issue.

4 - Mahani have made enemies over the last five millennia. 

These enemies target their children and families. An unhappy pack member who complains or gossips to another in a public place has resulted in people being tortured and killed many times. They have also had pack members work with the enemies to remove them from the pack as they feel they don't belong there or are jealous.

5 - Mahani come with emotional baggage. 

What they see and do is horrifying to most. Plus, they have been hunted and tortured for thousands of years. Quite a few of the current Mahani have been caught, abused, and tortured at some point because no one is perfect, and we all make mistakes.

I think Sam said it best:

"We may be the most powerful wolves alive, but we are not the greatest catch."