But that is the way it has to work. The preview file shows all of the adjustments that have been made using Lightroom. Lightroom doesn't apply changes to the original images. If there wasn't a preview than every time you load an image a new preview would have to be generated from scratch, and that would not be very practical. The preview files are much smaller, and you can choose from different preview sizes.
|Moon 99% D55 C14 St-Zénon 20170806 DP by MarioSS|
from Best Picture of the Week
|Reeds on lake by kkardster|
from Abstracts in Nature
|Florence & the Machine by Dutch Newchurch|
from Second chances..