Why is ignite on such a short cooldown?

Like i understand other combat summoner spells having low cooldowns, they are pretty telegraphed and only serve a single purpose, but ignite? Ignite is a 600 range point and click 70/410 TRUE DAMAGE that also provides vision and grievous wounds. Just the damage alone is already between 1/4 to 1/3 of most adcs HP in the game, but it ALSO denies the healing from their lifesteal AND their supports on a 180 second cooldown? Ghost offers you... movement speed on the same cooldown...
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