It looks like the Pipers were already powering up, possibly to taxi somewhere safer. Light planes like that can take off at very low speeds; stall speed for a Cessna 150 is only 60 knots, and with the engine already turning over, if they got a sufficient headwind they could pop aloft. The pilots probably decided it was better to take control and get some airspace, rather than risk getting bounced off the tarmac, repeatedly.
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