I think the article doesn't bother separating real motivations from stated motivations.
People want to have sex without consequences. That happens either in committed relationships or hookups. This gel does nothing for people who just want to hookup because of the risk of STDs. So you still have to use a condom anyway so why get the gel injection?
In committed relationships I could see it working. But committed relationships don't just spring up from nowhere. People who become committed probably started out doing this thing called dating where they tried to meet and sleep with people before settling down.
So women will use BC in both phases because it's the path of least resistance. I could see this working best as an alternative to vasectomy for a couple that is done having kids. But not as a replacement for condoms or female hormonal BC.