For years, Sarah Robinson was a faithful "Game of Thrones" viewer. Her loyalty to HBO, however, didn't run as deep.

Robinson, who works for a retail company in Houston, canceled her $15-a-month HBO Now subscription right before the last installment aired. The finale clocked a series high of 19.3 million viewers, according to HBO.

“It’s literally what I’ve done at the end of every season,” Robinson, 31, said.

It doesn’t take much digging through social media to realize that she’s not alone. “Game of Thrones” viewers around the country pledged — or threatened — to do the same, departing the cable channel roughly around the same time as its most popular series.

The potential wave of HBO cancellations puts the spotlight on what’s known in the industry as “churn,” in which users bail on a service — whether because of price hikes or the end of a global smash hit like the eight-season epic “Thrones.”

In an era of no-contract streaming packages and limitless content choices, television consumers are freer to roam than ever, soaking up shows on one service before jumping ship. The top entertainment companies, meanwhile, compete in an escalating battle for eyeballs and buzz.

“I think churn is a big challenge for an industry that was essentially designed to allow it, where viewers can switch easily between services and there’s very little barriers to entry,” said Brett Sappington, senior research director at the Dallas-based market research firm Parks Associates.

“What we’re seeing is that these companies are experiencing the other side of the sword,” Sappington added. “You’ve acquired all these users, but how do you retain them?”

The average subscription among leading streaming players lasts 31 months, according to new data shared exclusively with NBC News by Parks Associates.

That average length has increased over the last two years, the firm said — but it pales in comparison to the relatively longer and more consistent time periods that American consumers spend wrapped up in traditional cable bundles.

Netflix leads the pack when it comes to subscription retention, holding on to users for an average of 51 months, according to the data. HBO Now, the cable company’s direct-to-consumer streaming service, keeps users for less than half that — 18 months on average.

The market research group Mintel arrived at similar conclusions. The firm found that HBO Now users were twice as likely as those from any other top-tier streaming service to nix their subscription when a certain series — “Thrones” or otherwise — exits stage left.

Mintel’s data represents “potentially good news for Netflix,” Buddy Lo, a senior analyst at the firm, told Forbes. “Its presence as the leading [internet-based] streaming service is less sensitive to content-based cancellations than some may have thought.”

HBO, for its part, seems to be aware of the hazards. The pay-cable company has flooded its airwaves with clips and trailers for upcoming series, including big-budget adaptations of the seminal graphic novel “Watchmen” and the fantasy book series “His Dark Materials.”

The perennially Emmy-winning company also plans to roll out a slate of shows that might entice viewers outside the “Thrones” demographic, including the second season of the acclaimed ensemble drama “Big Little Lies” and the Spanish-language horror comedy “Los Espookys.”

“I do like to remind people in this moment when we’re so focused on ‘Game of Thrones’ just to remember that we do have a track record outside” the culture-conquering hit, HBO programming chief Casey Bloys told NBC News’ Dylan Byers last week.

“Thrones” might nonetheless be key to retaining subscribers down the road.

HBO in June will start shooting an untitled prequel series co-starring Naomi Watts, Bloys said — part of the AT&T-owned brand’s wider push to ramp up its original programming by 50 percent this year.

But the home of “Thrones” will face stiff competition from other premium channels working furiously to seize global attention with a fantasy show of similarly outsized scope and scale. Amazon, for example, plans to venture into Middle Earth with a television adaptation of the “Lord of the Rings” saga.

HBO has stood at a comparable fork in the road before. The era-defining mob drama “The Sopranos” wrapped up in 2007 — a virtual eon ago for an industry since reshaped by internet-based disruption — and left a hole in the channel’s Sunday evening lineup.

But news articles from the time don’t suggest the channel reported a drop-off in subscribers.

Robinson, the Houston resident who canceled her HBO Now account ahead of the “Thrones” finale, said she plans to take a hiatus from the cable channel for the next several months. She expects to re-up when the fourth season of the Issa Rae comedy “Insecure” debuts sometime next year.

“I’ll probably be back,” Robinson said.