: I assume there were a lot of factors working against Lego ever doing Halo
: toys, since Lego has Star Wars and it's both a bigger franchise and more
: explicitly kid-friendly, but my heart still wishes it came do be (I guess
: my wallet doesn't.)

Right in the 2010 Lego Corporate Responsibility Report, page 26:

Guideline for weapons and conflict in
LEGO experiences
A large number of LEGO minifigures use weapons,
and are – assumedly – regularly being charged by
each others’ weapons as part of children’s role play.
In the LEGO Group, we acknowledge that conflict in
play is especially prevalent among 4-9-year-old boys.
An inner drive and a need to experiment with their
own aggressive feelings in order to learn about other
people’s aggressions exist in most children. This in
turn enables them to handle and recognize conflict
in non-play scenarios. As such, the LEGO Group sees
conflict play as perfectly acceptable, and an integral
part of children’s development.

We also acknowledge children’s well-proven ability to
tell play from reality. However, to make sure to maintain
the right balance between play and conflict, we
have adhered to a set of unwritten rules for several
years. In 2010, we have formalized these rules in a
guideline for the use of conflict and weapons in LEGO
products. The basic aim is to avoid realistic weapons
and military equipment that children may recognize
from hot spots around the world and to refrain from
showing violent or frightening situations when communicating
about LEGO products. At the same time,
the purpose is for the LEGO brand not to be associated
with issues that glorify conflicts and unethical or
harmful behavior.

Linky

It does seem that this is changing with the introduction of themes like Star Wars, Indiana Jones, and the old Pirates and Western themes. None of those really involve warfighting except for Star Wars, and Star Wars has the benefit of being both fantastical and a monolithic cultural icon. For the more grounded and realistic designs of the UNSC, you'll have to look elsewhere.