There was probably one main reason why.
The Ford GT isn't something you see nearly every day like, for example, a Ford Escape. Ford's $450,000 sports car was meant to be rare from the get-go, and those fortunate enough to be offered the chance to purchase one had to agree to specific conditions (see: John Cena). Just over a year ago, however, Ford made the decision to extend GT production from 2020 until 2022. Demand was high and Ford figured limiting production to just 1,000 examples was not enough. As such, that figure has since been increased by 350 units, meaning the Ford GT's total 2016 to 2022 production run will now be 1,350 examples.
Ford's official 2019 sales report indicates was a very good year for GT sales. It seems the automaker made the right call to extend production. In the US alone, Ford GT deliveries increased by about 75 percent in the fourth quarter of last year for a total of 42 units. That figure was at 24 units at the same time in 2018. All told, 2019 GT sales increased by about 82 percent to 229 units compared to the year prior (126).
Again, these numbers are only for the US, but why such a significant jump from one year to the next? The likely reason is because GTs made in 2019 were mostly for buyers who were unsuccessful in the original selection process. If you recall, one had to apply for the chance to spend at least $450k on a GT.
Hopeful buyers had to convince Ford they were worthy to own one, or at least one from the first batch. Those selected received their cars a while ago, and now Ford is moving on to the next group which, it seems, is even bigger. The GTs slated to be built this year will be for new customers who placed an order following Ford's announcement to extend production. In general, Ford GT sales are actually quite small compared to others classified as sports cars.
For example, total 2019 Chevrolet Corvette sales came to 17,988 units. The Porsche 911 came next with 9,625 followed by the Mercedes-AMG GT (4,208), and Porsche 718 Boxster and 718 Cayman (3,880 combined). Even the BMW i8, which will cease production this May, sold 1,102 examples. However, the Nissan GT-R and Acura NSX were also towards the bottom at 331 and 238 units, respectively.
It's also important to point out that comparing Ford GT sales to any of those competitors isn't very fair because Ford manufactures and markets the GT in a very different way. It's also a lot more expensive, especially when compared to the C7 Corvette, which started at less than $60,000.