The problem with Gretna was that they didn't have a structure in place quick enough to be an actual contender to retain their place.
Airdrieonians were the same, they were liquidated near the end of the season if not after, and didn't have a structure in place to warrant a league place. Although they eventually bought their way back
I'm not entirely sure what the conversation about Clydebank being rejected is about, as never once have the been rejected membership to the SFL. In fact they're technically still a member
Rangers had the finances and structure in place to be a contender to stay in the leagues, and thier huge support base meant they'd be re-admitted even if it went to a vote. Just like, ironically, Clydebank. Who have been re-born three times in their history, twice being re-admitted to the SFL and once after Airdrie consumed their club and SFL status