Buy an option and the premium is the entire cost and the entire risk. Nothing further can be demanded of you.
Sell one and you receive the premium and post margin against a loss that is not bounded by it. That margin is recalculated as the market moves, so the position has an ongoing capital requirement rather than a one-off cost.
Why the requirement moves
Margin on a short option scales with how likely and how large the payout looks now. Spot moving toward the strike raises it; implied volatility rising raises it, even with spot unchanged.
That second one catches people. A seller can face a margin increase on a repricing alone — the vega exposure described in volatility of volatility, arriving as a capital demand rather than as a mark.
What crypto adds
Higher volatility means higher requirements, so the capital tied up per unit of premium is greater than the equity intuition suggests.
Settlement type matters. On a coin-settled contract the margin is in the coin, which reintroduces the reflexivity of coin-margined positions: the collateral moves with the thing you are short.
Portfolio margin changes the arithmetic entirely for a hedged book, per margined on risk, not on positions. A defined-risk spread can be workable under it and uneconomic without it.
The honest framing
Selling options is a business of collecting a premium that exceeds what gets realised — the comparison in implied versus realised. The margin is what lets you stay in that business through the periods when it does not.
Which makes the relevant question not the premium but how much capital must sit behind it, and how much that requirement can grow before you are forced to close.