Why? There are less voters in all Eastern states (Saxony, Saxony-Anhalt, Mecklenburg-Vorpommern, Thuringia, Brandenburg...) combined than in Laschet's North Rhine-Westphalia alone.* Their Chancellor preferences are of secondary importance for the federal elections. And always have been.
I don't like it but the CDU is the clear winner of this election. For at least four reasons:
(1) Defended the status quo in the last state election before September.
(2) Significantly overperformed their polling results and attracted many voters from SPD/Linke/etc.
(3) Proved that a clear anti-AfD strategy works (think of the Stahlknecht incident) - even in the East.
(4) Strengthened and secured Laschet's intra-party position.
This is literally the best imaginable scenario for the CDU.
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*I really think that this is a fact that cannot be highlighted often enough. Otherwise one can easily get a wrong (or at least distorted) idea of federal politics. The relative population difference between North Rhine-Westphalia and Saxony-Anhalt is roughly the same as the one between CA and AL.
I agree. It's a good result for them. I just don't believe that it's going to mean anything in 3 months. As you say, nobody in the west gives a lick of thought about the political wastelands of the East. A bad result could have been fatal for Laschet though.