Was there ever an explanation for why Mandalorian armor changed so much?

Question

Between the days of the Old Republic and Attack of the Clones, Mandalorian armor changed drastically. Here is what Mandalorians looked like in their old armor:

Here is what Mandalorian armor looks like now:

While I understand that armor may change over time, every Mandalorian save Mandalore himself wore the same kind of armor, so that armor must have become pretty important to their culture. This is what Mandalore looked like, you'll notice it's pretty similar to the modern armor but still quite a bit different:

I'm wondering if there was a particular reason why they changed armor, or if it's just something that quietly changed over time.

In canon, I don't think the old armor even existed, so I'm expecting answers to draw upon Legends. That being said, if there is something from canon that answers it, that would be a surprise to be sure, but a welcome one.

Answer 1

In Legends

Your first picture is of a Mandalorian Neo-Crusader. It is itself an evolution on the Mandalorian Crusader (below) armor which was was centered around defending its wearer during melee combat, which was considered by the Mandalorians to be the most honorable form of battle. The Neo-Crusader armor became the "standard" Mandalorian armor sometime during the Mandalorian Wars circa 3976 BBY.

Over time the "standard" Mandalorian Armor began drifting towards Mandalorian Shock Trooper armor. Which, you can see is moving back towards a lot of the same styles as the original Crusader armor. Likely a result of moving towards less melee focused warfare and the need for mobility over questionable protection (you can see a similar line of advancement in real world armor as bullets made full-plate armor a disadvantage). This is about the time the Mandalorians started adding various weapons to their suits of armor.

In Canon

Dave Filoni, Rebel's showrunner explained the evolution of the Mandalorian Armor

The Mandalorian-Jedi War that I have in my mind is very much derived from the oldest style of thinking of Mandalorians, which was that their weapons, their arsenal, their technology had a massive increase once they collided with the Jedi and found these force-wielding people that had abilities they didn't understand. Their armor is a reaction to the Jedi, and I've always believed that because that seemed to be something that would be in the DNA of the Joe Johnston [concept artist on the original Star Wars trilogy] designs of them as super commandos.

Their arsenal was very much designed to combat the Jedi. For example, I wouldn't know the details of the conflict that the fans have referred to. I played the video games though, so I'm aware of it in the games, and I like a lot of the things in there. So, when there are all these things in common and there's stuff that people know, I think 'Well, why don't we use that?'

_{From Interview with Comicbook.com}

So while the timeline is much more vague that in legends, the armor change is a result of a evolving to match their enemy.