Why does communism/socialism rely on a revolution to get into power...

That capital is worthless, you can print new one, equivalent of what escaped, so who cares. Moneyless is the end goal anyway.

More about fitting OP's criteria of bloodless revolution.

Because whenever a Socialist/Communist Goverment has the chance of being formed democratically (Chile'73 Russia'1917 Post-USSR Russia'96) its always either overthrown (Chile) Fucked up by Wreckers (Russia 1917) or the election is rigged against them (Russia 96)

If that ever happened, we would need to rethink all our criticism of reformism and liberal democracy.

can we count Allende? (I'm not sure if you want bloodless power-taking, including by electoralism, or if you want a bloodless revolution.)
granted he's basically the case study in why you should just have an actual revolution.

Seize the means of transportation.

The Bolivarian Revolution swept socialists into power in Venezuela without bloodshed. Unfortunately, it also ensured that the bourgeoisie were able to entrench themselves and strike back years later when the government was rocked by environmental crisis and low oil prices.

Which will require violence.

Because asking the ruling class politely for power guarantees you a grave or wishing you had one.

Shit son, get your game on.