Looking at the SRW sales, you can really see how the series has a problem. Year after year the sales of SRW are declining which is at odds with each new entry being more expensive if you want more detailed sprites and more animations.
The series was doing ~400k-ish starts during the PS2 days. Which dropped down to ~350k by Z1, and ~300k by Z2-1 so Namco figured "By splitting a mainline SRW in half, it probably costs 1.25-1.5x the cost of a normal game and we get 2x the profit", so as it fell to ~250k with Z2-2, combined Z2-1 & Z2-2 was more like 550k for what probably didn't cost a whole lot more than Z1 did on its own. But it still showed sales were on a decline, so they were probably more cautious with Z3's budget, and they were right (sales-wise at least) because Z3-1 is opening at around 280k and I wouldn't be surprised if following Z2-1 -> Z2-2's pattern, Z3-2 opens around 230k, which means combined they're doing a ~500k opening for Z3.
But obviously, Z1 and Z2's sprites and crazy animation quality was not cheap. So the question is if 500k opening -> ~750k lifetime with sales falling by about 30-50k an entry is going to keep being worth it for scamco.
The DLC will probably help a lot, because now if you want the "full Z3 experience" you'll need 2 games at 8000yen each + probably 4000yen of DLC each. So they could be looking at 750k lifetime sales for Z3, but at a much higher profit per copy than Alpha 3 or Z3.
So...for now by splitting the games in half and adding DLC, Scamco has probably kept the SRW mainline series profitable enough for the next half decade to justify big budget nice looking and nice sounding SRW (hopefully Z3-1 was just a rushed and isn't indicative of a drop in production quality. We'll see in Z3-2).
However if they're looking in the longterm of 10-20 years from now...the series is on its way out. There's not much more they can do to squeeze profit from the games at this point. Splitting them into 3 parts would probably pad them so much they'd lose fans, and any more than 24-30 maps for DLC would be kind of crazy. So from this point on the mainline profits are just going to drop and drop until the series is selling 100k, at which point the costs of licensing, voice actors, animations...won't be justifiable.
It's sad but the new generation of kids growing up in Japan playing pokemon and yokai watch don't seem to be interested in SRW. Maybe it's because mecha anime's become much less popular in the last decade so they haven't grown up on mecha. But the fanbase for SRW seems to be the same fanbase from the last 15 years who are just shrinking in number over time.
I know they add stuff like Miku to try to draw non-SRW fans in, but UX sales showed it didn't work. Not really sure how they can get more people in. Z2 had very popular series, great animations, was extremely accessible, but it still saw a decline.
I feel like Japan as a whole needs a couple Gundam Seed sized mecha anime hits once again to get kids into mecha and then have that be featured in SRW a few years later to help uptick sales again.