Most brokerages charge 7-9% for margin loans, so IBKR's rates are very low. But up to $100,000 of margin loans at IBKR costs 1.59%, nothing less. So if that $11M Twitter personality takes out an $80k loan, that costs them 1.59%.
https://www1.interactivebrokers.com/en/index.php?f=46376Keep in mind there's a mix of luck and skill in the stock market, and it takes a very long time to distinguish between the two. If someone invests in TSLA on margin, since Tesla didn't drop, they never had a margin call. So yes, they "never sold", because they got lucky.
To flip my investment style around for a moment, if someone invested everything in Macy's stock a year ago (Jan 2020), even going 1.5x on margin would have wiped them out. After Macy's stock dropped 75% in March, they would get a margin call, and their stock would be sold off - against their will - by IBKR. The proceeds would go to pay off the loan, leaving the investor with $0 left. Owing to the fast timing, they might even owe money. Picking a stock that never dropped, and never had a margin call, is lucky.
One side note, I mention Macy's a lot not because it's my only stock holding, but because I don't want to reveal all the others. Some of my stock holdings are so small and risky that, to quote Vanguard, they "have a 100% margin requirement", which means they don't count as an asset towards taking a margin loan.