Because Lexus says it doesn't have plans to replace it.
The Lexus F brand was launched back in 2007 with a performance sedan called the IS F. It was built until 2014 but was never replaced in the current IS generation, with Lexus instead opting to build a GS F sedan to rival the BMW 5 Series. Lexus has been rumored to finally replace the IS F with the next-generation IS, using the 3.5-liter twin-turbo V6 engine found in the LS 500.
A twin-turbo IS F sounds like an interesting prospect but according to a recent interview with CarSales, this rumor may be false. CarSales asked Scott Thompson, Lexus Australia's chief executive if plans for an IS F successor have been scrapped due to strict emissions regulations.
"How do I answer that question?" said Thompson. "It's one of my favorite cars that we've ever produced, [but] there are no plans at the moment" to build another one. The next-generation IS F was expected to arrive around 2022 but Thompson's words appear to have put the kibosh on these rumors. Lexus will eventually replace the current-generation IS with a new model, which will likely be based on Toyota's newer TNGA platform. Separate rumors have predicted Lexus could use a BMW-sourced turbocharged inline-six in the new IS, much like the one used in the Toyota Supra.
Few engines can replace Lexus' excellent 5.0-liter V8 but a BMW-sourced engine could produce around 380 horsepower, resulting in a healthy improvement over the current car. Thompson explained that the percentage of F cars Lexus sells is "smaller than our [German] competitors" but promises that performance will still be a part of the lineup moving forward.
Referencing the recently-revealed Lexus LF-30 Concept (pictured below), Thompson said there will still be sporty vehicles from Lexus in the future. "I think Australia is definitely a market that loves its sports variants and performance vehicles, and I think what you've seen in terms of 'posture control', as they've called it … you'll see the performance opportunities that deliver in terms of our vehicles, and I think the F brand will be very much a part of that," he said.
"Posture control is bigger than just simply propulsion. It's about what electrification can deliver to the vehicle in terms of its performance. Posture control looks at the adaptive nature of the vehicle - turning as well as propulsion and other aspects to improve performance," Thompson explained. "I can't definitively tell you about the time frame, but in terms of the LF-30, some of those technologies you've seen and heard about will come well inside that  timeframe."
"We want to make the driving experience more fun, re-engaging the driver. This type of tech is supposed to learn with you, grow with you, and improve your ability as a driver," he added. It remains to be seen how this technology will be integrated into the Lexus lineup moving forward but it seems clear the F brand may be very different in the near future.