Microstrategy does not buy Bitcoins with its own funds, but with funds received from issuing bonds and shares.
That's why they follow this strategy because they believe that the price of BTC will surpass any fiat debt. If BTC rises, they will sell less in order to pay their fiat debt.
The management of Microstrategy is experienced Wall Street businessmen. These people are not guided by emotions, but by rational calculation.
Well, those people said that BTC is a bubble...

Anyway, they calculate the positive scenario. Did they calculate the negative possibility as well? BTC isn't a stock...
Bitcoin is a deflationary asset and it grows over time. Currently, the idea of creating Bitcoin reserves is actively discussed in the United States. In the future, all countries will have Bitcoins as part of the gold and foreign exchange reserves of their Central Banks. Bitcoin is gradually becoming a strategic reserve.
And probably, that's the reason that they don't be afraid to buy aggressively. Because they know that these moves will be made and will make the price rise even more. If Governments see it as a reserve, that means that they will not trade it instead they will hodling it.