Is there a reason to why most chapters go with ballistic weaponry over other forms of weaponry?
Like why aren't more chapters using plasma weapons, laser weapons or meltas? Most chapters rely on bolters and heavy bolters and so on.
While Marduk's is the technically correct one, I think the more accurate answer is somewhere in the realm of game balance. Sure, plasma weapons are complicated and hard to build in universe, but you'd think after 10,000 years a couple chapters would have been able to stockpile enough of them they could hand them out to everyone (maybe not all the time, but they could have some kind of Oprah protocol for emergencies: "You get a plasma gun and you get a plasma gun and you you get a plasma gun! Plasma guns for everyone!").
As far as lasers go, only hellguns can approach bolters in power lorewise, and they still lose out and are, IIRC, actually less reliable and more maintenance intensive than bolters.
Laser weapons do not need ammunition as they generate their ''projectile'' so it'd make logistics a lot easier as laser only requires power source. Meanwhile with bolters you need power source for bolter (as I've read that they have internal targeting systems and so on...) plus ammo.
Marines, generally speaking, tend to stick to short high intensity conflict where they can make a decisive win before logistics become a factor. And aside from that, lasers being logistically easier comes at a massive tradeoff in firepower. Lasguns might be easy to keep loaded in the long run, but they just can't compare to bolters when it comes to per shot lethality, which the marines need far more than they do easy resupply.
How about using lower quality plasma? How would that go? Certainly not packing that much punch as they could, but the wider availability across the chapters would be the payoff for this tradeoff.
I would assume they don't find the tradeoff worthwhile. We know the guard has plenty of power and plasma weapons, enough that if they were given to marines instead they could have them for most of a chapter, but I presume that the quality and reliability of those weapons is sufficient poor that the marines don't feel it's worthwhile (or it's not possible to swap thing around like that. Perhap in the process of making a guard quality power sword strong enough to handle being swung around by a marine, the added cost of making a more rugged sword means it's no longer feasible to build them in the same numbers).