Why does the management group get Modify and not Full Control on its folder?

Question

Accepted Answer

Modify covers everything a user needs for their work (read, write, create, delete files); Full Control adds the right to change permissions and take ownership, which belongs to administrators.

Right
Modify
Full Control

Read, list, execute
yes
yes

Create, change and delete files and folders
yes
yes

Change permissions
no
yes

Take ownership
no
yes

A user with Full Control can quietly add anyone to the access list, or remove the admins, which puts the permission concept out of the administrators' hands. Modify is therefore the usual ceiling for business users, in line with least privilege.
Go deeper:

TechNet Magazine: NTFS Permissions, Part 2 — standard vs. special permissions, and a department example with managers on Modify.

Right	Modify	Full Control
Read, list, execute	yes	yes
Create, change and delete files and folders	yes	yes
Change permissions	no	yes
Take ownership	no	yes