Why is Kvitova prematurely ending in Wimbledon since 2015?

[Enceladus]

At its best GS tournament, Kvitova finished fourth in a row in the first week. After her second triumph (2014) she did not come to the QF in subsequent years. Why? I miss last year when she returned to tour after a brutal assault.

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Hall of Fame Open (Newport)
Adrian Mannarino (def. Alex Michelsen 6–2, 6–4)

Swedish Open (Båstad)
Andrey Rublev (def. Casper Ruud 7–6(3), 6–0)

Swiss Open (Gstaad)
Pedro Cachin (def. Albert Ramos Viñolas 3–6, 6–0, 7–5)

Hamburg European Open
Alexander Zverev (def. Laslo Djere 7–5, 6–3)

Atlanta Open
Taylor Fritz (def. Aleksandar Vukic 7–5, 6–7(5), 6–4)

Croatia Open (Umag)
Alexei Popyrin (def. Stan Wawrinka 6–7(5), 6–3, 6–4)

Washington Open
Dan Evans (def. Tallon Griekspoor 7–5, 6–3)

Los Cabos Open
Stefanos Tsitsipas (def. Alex de Minaur 6–3, 6–4)

Generali Open Kitzbühel
Sebastián Báez (def. Dominic Thiem 6–3, 6–1)

Canadian Open (Toronto)
Jannik Sinner (def. Alex de Minaur 6–4, 6–1)

Western & Southern Open (Cincinnati)
Novak Djokovic (def. Carlos Alcaraz 5–7, 7–6(7), 7–6(4))

Winston-Salem Open
Sebastián Báez (def. Jiří Lehečka 6–4, 6–3)

US Open (New York City)
Novak Djokovic (def. Daniil Medvedev 6–3, 7–6(5), 6–3)