So I did some research and found the best explanation for the problem. Please note that this is not my explanation, but it comes from Charles E. Snyder III, a web designer/content manager.
"The reason is that the Android Gmail app does not render HTML when composing. It can read it just fine and there are ways to get your signature into an email, you just need to know how.
But why would they do this when so many people have been asking for it over the years? Not making excuses and I have yet to find a straight answer to that question, but I can tell you that it usually boils down to security. In other words, it is damn near impossible for someone to send malicious code in a plain text email. It’ll have to be added as some form of attachment.
But on to answer your question… The easiest way is to create the desired signature(s) in Gmail and share them via Google Drive with your devices from a unique folder, such as “Signatures.” Once you got this setup, then it is simply a matter of adding the URL of your Google Drive Signatures folder to your Android phone Gmail App via the setup menu.
Here’s how to your company logo or signature image, step-by-step:
Host your image on Google Drive
Log in to your Google Drive account
Create a folder, name it Signature or something like that
Select the folder and click on the Sharing button; set the folder visibility to Public and the access to anyone can view
Open your folder and upload your image, or add an existing one to the folder. The image will take on the Public visibility.
Copy the folder’s ID from the address bar, and build up the URL to include the folder ID and the image name.
Set up your signature
Open Gmail, click on the cog icon thingy and choose Settings
Paste in the image URL you built above and your company logo should appear in the box next to Web address URL, click OK
You should now see your logo in your signature
Scroll down to the bottom and save your settings
Send yourself or a coworker an email to test it has worked!"