We are trying to find a good solution for this! It's tougher than it seems. As noted by others, the LSTAR uses ammo in a different way. Most guns have ammo on pickup because the ammo in the magazine doesn't count towards ammo in your inventory, so they can spawn with a full mag and not have it affect your inventory at all. The LSTAR's ammo count is just the amount of ammo you have in your inventory, so if you pick it up with no ammo in inventory, then it's 0 which stinks. Hopefully it's not a problem every time much because guns have their ammo spawn next to them, but it definitely is too common that you get one with 0 ammo and can't use it, which sucks.
There are a few solutions that seem possible but have some pretty big problems that make them untenable. The most obvious one is "what if you got free ammo in your inventory when you picked up an LSTAR?", but then people could get infinite ammo! This leads into "what if the LSTAR only gave the ammo when it was picked up the first time?", but this encourages some weird and unfun play patterns. Remember, when you are finding an LSTAR on the ground with no ammo around it, that's because another player has come along and wanted the ammo but not the gun, so they scooped up the ammo. Since they want the ammo, we are just encouraging anyone running a volt to have to pick up LSTARs and immediately drop them for the ammo. This is obviously frustrating since you may have to drop a gun and all it's attachments then repick it all back up, and it's just a bizarre and clunky thing to do when we've done so much work to make looting streamlined and fluid. Additionally, now some LSTARs will give you ammo when you pick them up, and some won't, since some LSTARs will have been touched by other players and some not. It'll be super inconsistent and confusing, and that'll make it hard for most players to understand, since they don't come on reddit or read patch notes or anything. "What if the LSTAR gave ammo but only the first time it was picked up _per player_". This doesn't solve the degenerate use case of needing to pick up and drop LSTARs for the ammo, and it may cause worse things where a team passes around the LSTAR to each other to get max ammo then moves all the ammo to someone. "What if it was _per squad_?". This still doesn't solve the big issue of the weird use case. "What if it only gives ammo one time per squad and it only gives ammo if you don't have energy ammo already or another energy gun or..." at this point, the design alarm bells are ringing. This solution is just getting far too complicated and special case-y. Almost no players will be able to understand or figure out the rules of how it works, and the whole point is to make picking up the LSTAR and immediately using it consistent and smooth -- this is just making things inconsistent and weird and complicated. In general, when a design solution starts having to make tons of minor conditional adjustments to meet tons of special cases, that's just an indicator that it's not a good or elegant solution. For these reasons, we decided to steer away from that sort of stuff.
HOWEVER, we have some other ideas! There's one that we think is a decent solution, it has some weirdness but I think it's worth it for the benefits. But, from the technical side, it gets pretty hairy and has the potential for lots of bugs. The problem is fundamentally due to the fact that the various ammo systems are coded differently and are built for very specific purposes, and we want to do some sort of weird hybrid between 2 of them and pick and choose pieces from each. This requires some technical rework and needs to be done right, we can't just hack this in real quick due to the risk of how much stuff has to be touched, and in general there's a lot of UI and gameplay adjustments and such that needs to be changed to make this work. Think of everywhere in the game where the game is dealing with how to move around and mess with ammo, and then realize that there's tons of places it happens that you probably don't even realize on the surface (guns on the ground aren't the same entity type as a usable weapon, ammo boxes on the ground aren't the same as ammo in your inventory, which isn't the same as ammo in your gun, etc.). We have some initial work done, but it wasn't ready for the next season launch. We're working on it though!