Why doesn't Windows 7 always create 100MB partition?

Solution 1:

This “stub” of a partition, which is new in Windows 7, serves two functions. First, it holds the Boot Manager code and the Boot Configuration Database.
Second, it reserves space for the startup files required by the BitLocker Drive Encryption feature. If you ever decide to encrypt your system drive using BitLocker, you won’t have to repartition your system drive to make it possible.

Understand (and Get Rid of) the Mysterious Small Partition

I really don't understand why it wouldn't be created if you install to the first drive, unless you have a pre-existing partition on it. Usually, the partition is always created on an empty drive for the reasons quoted above.

Solution 2:

That partition must always be created mostly in the primary drive (master) since it contains the boot loader and all boot configuration stuff, but it is normally not created during normal disk-formatting on other drives/hardisk. It will be created if you format a drive or partition as drive as primary partition. As can be seen with diskpart's create partition primary <----- here goes your 100mb boot partition.

Solution 3:

The 100 MB partition is used to store some boot info and as a store for essential files for Bitlocker encryption. There are complex ways to get rid of it, but in most situations it would not be worth the effort to free up 100MB.