You can picture ablaze as one thing wrapped in fire from end to end. Not a corner catching, not a single small flame, but the whole surface giving off light and heat at once, so that anyone looking from a distance sees it glowing. Everything the word does grows out of that one wide, burning picture: first real fire, then anything that looks like it, then anything that feels like it.
From the word’s history
Wiktionary analyses ablaze as a- (on, in) + blaze (flame), literally in flame. That matches the way the word behaves today: it names a state something is in, so it sits after be or set rather than in front of a noun.
Wiktionary 把 ablaze 拆成 a-（在…之中）加上 blaze（火焰），字面就是「在火焰裡」。這和它今天的行為對得上：它講的是一個東西「處在什麼狀態」，所以放在 be、set 後面，而不是放在名詞前面。
Wiktionary entry for ablaze, kaikki extract kaikki:3f6f69a190036ae4:11897538:20393 (etymology: a- + blaze)
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