Ingenuity is a low cost technology demonstrator. As a technology demonstrator, NASA and JPL cut lots of corners to keep the cost low (low by NASA standards, only \$80 million US compared to the \$2.2 billion cost for the rover). Ingenuity was planned to make just five flights during the first few months of the mission. If it had fallen short of this goal of five flights by a flight or two it probably would still have been deemed a success. It successfully completed those first five flights, with one incident from which recovery was possible. It has since made eight additional successful flights, far exceeding expectations.
It transitioned from being a mere technology demonstrator to being an operational aid after that fifth successful flight. "Operational aid" means it can be used in a non-mission critical sense to help scout paths for the rover and to scout targets of interest. It will never be made mission-critical; it was not designed for that. It was designed as a technology demonstrator.
One of the corners that was cut was to design for the benign atmospheric conditions that were expected in the few months after landing. Designing and testing for the not so benign atmospheric conditions many months after landing would not have been consistent with the technology demonstrator nature of the project. Doing so would have increased the costs by quite a bit, and it wouldn't have made sense.
Since Ingenuity has proved the viability and usefulness of a Mars helicopter, possibly sacrificing it to see if can survive making the rotor spin so fast that the blade tips are moving close to speed of sound makes sense. The helicopter will be essentially dead if the change isn't made, and may well be dead if the change results in a failure.
But if it succeeds, the helicopter can be continued to be used as an operational aid -- at least until the helicopter fails, possibly for some other reason. That failure (and it will fail eventually, almost certainly well before Perseverance fails) will not detract from what Ingenuity has already done.
Why not wait?
A comment suggested to save Ingenuity for better weather in the future. That would be a very long wait. The graph below shows why waiting is not an option.
Source: Trainer, Melissa G., et al. "Seasonal variations in atmospheric composition as measured in Gale Crater, Mars." License: CC BY-NC 4.0
Perseverance landed on Mars on February 15 2021, about a week after the northern hemisphere spring equinox. The atmospheric pressure on Mars rises for about 100 days after the spring equinox. That made for ideal flying conditions.
But then atmospheric pressure began to fall. By the northern hemisphere summer equinox on August 25, 2021, the fall was in full decline, and will continue to decline for the next 100 days or so after August 25. The atmospheric pressure will remain below the August 25 level for another 100 days after the late summer minimum.
Since transmission of commands to and data from Ingenuity requires relativity close proximity to Perseverance, waiting would require the rover to remain near its current location for the next five months. That would be highly counterproductive to the overall goals of the rover's mission. Waiting is not an option.
Trainer, Melissa G., et al. "Seasonal variations in atmospheric composition as measured in Gale Crater, Mars." Journal of Geophysical Research: Planets 124.11 (2019): 3000-3024.