Difference between 1TB USB stick and 1TB external SSD ?

Hi,
What is the difference between 1TB USB flash drive and 1TB external SSD ? Why is USB flash drive cheaper ?

External SSDs usually have higher file transfer speed than USB flash drive. So if you need to often upload or download files, then SSD will be a better option.

USB sticks with higher storage space can get quite warm when transferring the files.