Why is wd.switch_to.default_content() not returning to original webpage?

I'm making an image scraper for bing because it has a well developed search by license function. In anycase I can't seem to get more than one image because I can't get back to the main page after switching to the iframe to get the src from the first image. Any tips?

    import selenium
    from selenium import webdriver
    from selenium.webdriver.support import expected_conditions as EC
    from selenium.webdriver.common.by import By
    from selenium.webdriver.support.ui import WebDriverWait
    
    image_url = []
    
    wd = webdriver.Firefox()
    
    wait = WebDriverWait(wd, 10)

    ##search bing for images
    search_url = f"https://www.bing.com/images/search?q=cat%20clipart&qs=n&form=QBIR&qft=%20filterui%3Alicense-L1%20filterui%3Aimagesize-large&sp=-1&pq=good%20clipart&sc=8-12&cvid=493F746CDC7B4E70BF3BEDDA3CF674E1&first=1&scenario=ImageBasicHover"
        # load the page
    wd.get(search_url)
    
    thumbnail_result = wd.find_element_by_css_selector("img.mimg")
    
    thumbnail_result.click()
    
    wait.until(
            EC.frame_to_be_available_and_switch_to_it((By.ID, "OverlayIFrame"))
        )
    wait.until(
            EC.presence_of_element_located((By.CSS_SELECTOR, "img.nofocus"))
        )
    
    actual_image = wd.find_element_by_css_selector('img.nofocus')
    
    image_url.append(actual_image.get_attribute('src'))

    ##This is where it doesn't switch back to the original webpage    
    wd.switch_to.default_content()

Here is the code with the changes you suggested:

import selenium
from selenium import webdriver
from selenium.webdriver.support import expected_conditions as EC
from selenium.webdriver.common.by import By
from selenium.webdriver.support.ui import WebDriverWait

image_url = []

wd = webdriver.Firefox()

wait = WebDriverWait(wd, 10)

search_url = f"https://www.bing.com/images/search?q=cat%20clipart&qs=n&form=QBIR&qft=%20filterui%3Alicense-L1%20filterui%3Aimagesize-large&sp=-1&pq=good%20clipart&sc=8-12&cvid=493F746CDC7B4E70BF3BEDDA3CF674E1&first=1&scenario=ImageBasicHover"
    # load the page
wd.get(search_url)

wait.until(EC.element_to_be_clickable((By.CSS_SELECTOR, "img.mimg"))).click()

wait.until(EC.frame_to_be_available_and_switch_to_it((By.ID, "OverlayIFrame"))
    )
wait.until(EC.presence_of_element_located((By.CSS_SELECTOR, "img.nofocus")))

actual_image = wd.find_element_by_css_selector('img.nofocus')

image_url.append(actual_image.get_attribute('src'))

print(image_url)

wait.until(EC.element_to_be_clickable((By.CSS_SELECTOR, "div#close"))).click()

wd.switch_to.default_content()

wait.until(EC.element_to_be_clickable((By.CSS_SELECTOR, "img.mimg"))).click()

wd.switch_to.default_content() not return you back to main page .It is used to come out from iframe.You need to click on close button to close the image page. Once you click on that you'll see main page

image_url.append(actual_image.get_attribute('src'))

#Click on close button to go back to main page
wait.until(EC.element_to_be_clickable((By.CSS_SELECTOR, "div#close"))).click()

##Now jump out from iframe
wd.switch_to.default_content()