If we take the timeframe between 1989 and 2001:
Capcom released around 60 arcade games across 6 different hardware platforms.
Sega released over 150 arcade games on at least 9 hardware platforms.
SNK released about 140 games on just 2 hardware systems.

SNK had some strong years with KOF ‘97 and ‘98, and some good months with SamSho and Garou. But Sega and Capcom absolutely dominated the arcade scene for nearly two decades. Even Namco and Taito eventually gave up trying to catch up.

Sega and Capcom were printing money, releasing multiple games of exceptional quality and cutting-edge technology. Even their older titles were still profitable (Final Fight was in the top 10 in 1993 on some months).

Capcom was so confident they charged around ¥80,000 for a single new B-board exchange (2X or Dungeons & Dragons). A brand-new CPS2 A+B set was priced around ¥170,000 ¥200,000.
Sega was selling theirs for roughly double that but for good reasons.

For SNK to make the same money, they had to sell five or six of their most expensive MVS games. They crashed and burned once they tried to create their own 3D hardware to compete with Sega (not even Capcom was reckless enough to do that). At the same time, Sega released a “better MVS,” capable of everything at the highest resolution for the lowest cost

Naomi kit was ¥80,000 ¥100,000, and a complete kit cost about the same as a CPS2 set.

In the end, SNK had good games and a couple of strong licenses, but they lacked the technology, quality, and originality of Capcom and Sega. Most of their catalog was just “good enough” to play while waiting for the big releases.