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I wonder why I suddenly started getting frozen out halfway through.
Literal
Why partway [from-から] suddenly be-frozen-out [come-to-ようになって]-[regret-しまった]-[explanation-んだ]-[wondering-ろうか].
干される 'to be dried' is used in the entertainment-industry idiom for 'to be frozen out' — denied work, no longer being called on. The passive is obligatory for this idiom. ~ようになる 'come to (be able to / do) X' marks a change-of-state transition. Stacked: 干される (passive) + ~ようになる (change) + ~てしまう (regret) + ~んだろうか (hedged wondering) = 'I wonder how I ended up getting frozen out.'