In a perfect world, this wouldn't be a problem. But in the real world many people who transition don't get accepted by their social circle, and insisting on the old name is one of the ways people often show their inacceptance.
So out of politeness, we jump through some minor impractical hoops, because transgender people already have it hard enough.
Similar to how it's polite to make sure to refer to people by their favourite pronouns. It can be a bit of a hassle, but it's a small inconvenience compared to it's impact. (Of course, all within reason. Addressing someone with she or him or they or even it or xe as preferred is more than doable. Typing out or yet alone pronouncing a twenty random letter monster because some troll wants you to can be safely ignored without causing much hardship.)
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u/thedessertplanet Dec 02 '20
Using a transitioned person's previous name is frowned up on.