This is because selenium doesn't use your default browser instance, it opens a different instance with a temporary (empty) profile.
If you would like it to load a default profile you need to instruct it to do so.
Here's a chrome example:
from selenium import webdriver
from selenium.webdriver.chrome.options import Options
options = webdriver.ChromeOptions()
options.add_argument("user-data-dir=C:\Path") #Path to your chrome profile
w = webdriver.Chrome(executable_path="C:\Users\chromedriver.exe", chrome_options=options)
And here's a firefox example:
from selenium import webdriver
from selenium.webdriver.firefox.webdriver import FirefoxProfile
profile = FirefoxProfile("C:\Path\to\profile")
driver = webdriver.Firefox(profile)
Here we go, just dug up a link to this in the (unofficial) documentation. Firefox Profile and the Chrome driver info is right underneath it.
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