D&D 5E Why do 5e lycanthropes get their powers in human form?

[Cap'n Kobold]

For reference MM page 207:

PLAYER CHARACTERS AS LYCANTHROPES
A character who becomes a lycanthrope retains his or her statistics except as specified by lycanthrope type. The character gains the lycanthrope's speeds in nonhumanoid form, damage immunities, traits, and actions that don't involve equipment. The character is proficient with the lycanthrope's natural attacks, such as its bite or claws, which deal damage as shown in the lycanthrope's statistics. The character can't speak while in animal form.
A non-lycanthrope humanoid hit by an attack that carries the curse of lycanthropy must succeed on a Constitution saving throw (DC 8 + the lycanthrope's proficiency bonus + the lycanthrope's Constitution modifier) or be cursed. lf the character embraces the curse, his or her alignment becomes the one defined for the lycanthrope. The DM is free to decide that a change in alignment places the character under DM control until the curse of lycanthropy is removed.
The following information applies to specific lycanthropes.
Werebear. The character gains a Strength of 19 if his or her score isn't already higher, and a +1 bonus to AC while in bear or hybrid form (from natural armor). Attack and damage rolls for the natural weapons are based on Strength.
Wereboar. The character gains a Strength of 17 if his or her score isn't already higher, and a +1 bonus to AC while in boar or hybrid form (from natural armor). Attack and damage rolls for the tusks are based on Strength. For the Charge trait, the DC is 8 + the character's proficieny bonus + Strength modifier.
Wererat. The character gains a Dexterity of 15 if his or her score isn't already higher. Attack and damage rolls for the bite are based on whichevers higher of the character's Strength and Dexterity.
Weretiger. The character gains a Strength of 17 if his or her score isn't already higher. Attack and damage rolls for the natural weapons are based on Strength. For the Pounce trait, the DC is 8 + the character's proficiency bonus + Strength modifier.
Werewolf. The character gains a Strength of 15 if his or her score isn't already higher, and a +1 bonus to AC while in wolf or hybrid form (from natural armor). Attack and damage rolls for the natural weapons are based on Strength.

How do these rules differ from the ones given in the Strahd and Candlekeep books if they are actual PC options in them?

Except that were-ravens are presented as pc options in both Strahd and Candlekeep.

As a monster I don’t care but as a pc? That’s ridiculous.

 

[Voadam]

How do these rules differ from the ones given in the Strahd and Candlekeep books if they are actual PC options in them?

Strahd just adds wereraven as a new afflicted lycanthrope subtype to the list in the MM using the same basic rules.

CoS page 242:

Characters as Wereravens. The Monster Manual has rules for characters afflicted with lycanthropy. The following text applies to wereraven characters specifically. A character cursed with wereraven lycanthropy gains a Dexterity of 15 if his or her score isn't already higher. Attack and damage rolls for the wereraven's bite are based on whichever is higher of the character's Strength and Dexterity. The bite of a wereraven in raven form deals 1 piercing damage (no ability modifier applies to this damage) and carries the curse of lycanthropy; see the "Player Characters as Lycanthropes" sidebar in the lycanthropes entry in the Monster Manual for details.