What was with this show's general fascination with Japan

[TMC]

Julia and Suzanne's mom, Perky ups and moves to Japan. One of Charlene's first boyfriends (Mason) ups and leaves Atlanta for Japan. And finally, Suzanne Sugarbaker herself moves to Japan.

[cbikle]

Hmm. Maybe Japan was a big part of the furniture design business back then and/or, Japan was just on the minds of the showrunners.

Around that time period, Japan was a HUGE financial powerhouse and businesses from that region were aggressively buying U.S. businesses, especially those in the entertainment/media sector.

[TV Guy]

It’s like Europe on Dallas. Whenever they wanted to write out a major character (Ray, Sue Ellen, Jenna, Lucy, Ellie, Clayton), they packed them off to Europe. I guess it was a way to easily explain why these people didn’t come home for later family events. But it seemed a little silly.

[hch]

The recurring theme of Japan in Designing Women was less about furniture design and more a reflection of the era’s socio-economic climate and the practical needs of sitcom writing.
Here is why Japan became the show's go-to "off-screen" destination:

The "Japan Inc." Era: During the late 1980s, Japan was a global financial powerhouse experiencing a massive economic "bubble." It was frequently in the American consciousness as a land of limitless prosperity and high-tech influence, making it a trendy and exotic location for characters to chase new business ventures or luxury items.

A "Polite" Way to Fire Characters: When characters needed to be unceremoniously removed due to behind-the-scenes drama, Japan served as the ultimate "Put on a Bus" destination.

Perky Sugarbaker: Julia and Suzanne’s mother moved there early on, which established the country as a familial "home away from home".
Suzanne Sugarbaker: After Delta Burke’s highly publicized feud with producers, the writers simply had Suzanne move to Japan to live with Perky. It was far enough away that the character could be permanently gone but close enough (emotionally) to visit off-screen.

The "Big Adventure" Episode: The show leaned into the trope with the Season 4 episode "Julia and Suzanne's Big Adventure," where the sisters travel to Tokyo. This episode used the cultural setting for comedy—including Suzanne insulting passengers on the plane and the sisters being robbed at the airport before getting stranded in a "capsule" hotel room.

The "Europe on Dallas" Effect: Just as you noted with Dallas, sitcoms often use a distant, wealthy location to explain why a character isn't just "in the next town over." If Suzanne had moved to Alabama, fans would ask why she didn't come back for Julia’s birthday; if she's in Tokyo, her absence is easily excused.

By the time Suzanne returned for her spin-off, Women of the House, she had left Japan behind to move to Washington, D.C., signaling that the "Japan" phase of the Sugarbaker lore was officially over.