Bandai isn't magic, they just cheat.
IMO it's not a matter of "magic" - it's simply Bandai chooses to accept a different set of compromises than most other kit manufacturers.
For instance, if you look at a Kotobukiya Armored Core kit: Specifically the C75 "Close Combat Type" - the chest on that thing is basically a big blue block. There's details, there's facets, but you could think of the thing as a big blue rectangle and not be too far off.
Now, despite this, the part is built up out of not just two or three parts, but actually something like twelve parts, just for the blue bits of the chest. The reason for this is that when parts are injection-molded, the steel molds have to be removed along a single direction: thus, parts can't have undercuts relative to the direction (or directions) in which the mold parts are separated. So to mold a part with detail on all sides of it, you need to either split the part into multiple, smaller parts (thus introducing seam lines) or else use more than two parts in your mold. The latter technique is used by various manufacturers including Bandai. It tends not to be used for most parts, however, because of the extra cost and complexity it adds to the model's mold.
But because Bandai prioritizes ease of assembly and cost-cutting above detail on their main-line Gundam models, they don't usually break down parts into too many smaller parts unless there's a color boundary. Instead they'll mold that detail from an unfavorable angle (for instance, the panel lines on the old Master Grade Zaku and Gundam, and many other Gundam kits for that matter) giving panel lines a poorly-defined appearance - or change the detail to suit their mold designs, or omit it altogether.
In general with Gundam kits, Bandai tends to adjust the design to fit the model production rather than the other way around. If they have a seam line between a couple parts, they'll introduce a panel line that coincides with the location of that seam. This gives them a huge advantage over manufacturers who choose to represent an existing design faithfully.
From my perspective it's Bandai who's "cheap" - not as in "stingy" but in the sense that they cheat - with the Gundam line at least. In a more general sense, their ideas of what make a good model kit don't generally jive with mine.
Of course, not everything Bandai makes is Gundam. They have even made models of properties over which they do not hold creative control of some kind... For instance, their Star Trek kits (from what I've heard, these are notoriously problematic in their parts fit, prone to light leaks in the gaps that form, etc.) I don't know of other examples offhand, of what happens when Bandai makes kits of non-Bandai, non-Sunrise properties...