Except in WC3 and SC they managed to create completely different armies.
The thing is, blizzard NEVER implemented new armies after initial release of their RTS.
Starcraft's races are actually very similar in design even though they're very unique in how the design is implemented. You can boil down the core design of every Starcraft faction (going off of SC2 here) as having the following attributes:
Workers that harvest resources and build buildings.
Tech buildings that are required before certain units can be produced, and buildings to produce those units from.
Three levels of offensive and defensive upgrades for all fighting units.
A central method of boosting economy/production.
A mix of fighting units and harassing units.
A method of health regeneration for units and buildings.
All three SC2 races have that same design. How that design is implemented in the different races is very different, of course. Health regen, for instance, is passive over time for Zerg, limited to shield regen for Protoss, and achieved through healing and repairing units for Terran. Upgrades are separated into ground and air for Protoss, melee and ranged for Zerg, and bio and mech for Terran. Production boosting occurs with Chronoboost for Protoss, larva injection for Zerg, and mules for Terran.
Even though the Starcraft factions may seem vastly different from one another, they actually share a ton of core design details. A big problem with Company of Heroes factions through the life of the franchise is the lack of central design details guiding faction design.
For instance, look at Americans vs. Wehrmacht in CoH1. The core design details in that matchup are flanking, suppression, and drawn-out engagement. Now, CoH is an asymmetrical game, so you're not going to see the direct similarities that you see in a symmetrical game like Starcraft, but you can still draw some comparisons. Suppression encouraged flanking, and the soft-counter nature of vanilla units encouraged long, drawn-out engagements, both of which combined to make for an experience that people latched on to and really enjoyed.
Now try to find those same design details in the Opposing Fronts factions. All of a sudden flanking and suppression are pretty much thrown entirely out the window. PE doesn't have a reliable suppression unit, so there's not going to be any flanking in that matchup, and Brits have no reason to bother with flanking when they have a powerful, hardened long-range mortar structure, Heroic Charge, and infantry units that move slowly in enemy territory. Furthermore, you have units like Commandos and Armoured Cars that are able to get nearly anywhere on the map extremely quickly and wipe entire squads with little warning. Suddening the long, drawn-out engagements are a thing of the past as well.
This is what I mean when I say the OF factions were poorly designed. There were other things that they retained, like upgrades and veterancy, but ultimately it didn't really matter because the act of actually playing the new factions was so divorced from what made the vanilla factions so great. They completely neglect three of the core design details that made the original vanilla CoH1 matchup so iconic. The CoH2 factions suffer from the same problem, neglecting things like global upgrades that gave CoH1 its competitive longevity. Instead of sticking to the core formula that made the original factions so amazing and then iterating on them, Relic has historically attempted to create entirely new armies with little regard for what makes an army fun and interesting in the first place.