Why does gmail remove inline styles for p?

Question

css

Good afternoon!
There is an html signature made with heml , which is correctly displayed when sending a letter directly (via php) in all email clients. Now you need to insert it as a signature in the mail client (Thunderbird), which was done, however, when sending a letter, gmail removes all inline styles (font size, boldness) for p elements (and span too), while other mailers (for example, mail. ru) display everything correctly. What could be the reason for this, because inline styles are allowed, who knows, please tell me.
PS In the original gmail letter there is markup with all inline styles

UPD:only a holy war will help against mailers, because. they do what they want without explanation. The reason was that, among other inline styles, font-family was specified, i.e. for all elements for which fonts are specified (with fallback) ALL styles have been removed. If you remove the font-family rules, then the styles will be saved