I only have my work Slack, not email, on my phone because of this. Something I've wondered: why do they only do this for native email? Why can I use Slack with

I only have my work Slack, not email, on my phone because of this. Something I've wondered: why do they only do this for native email? Why can I use Slack without it? In college even our student email accounts had MDM (which was pretty silly), but I worked around it by just viewing my email in the web browser. Are locally-stored emails somehow more vulnerable than my browser cache and the messages stored in the Slack app, or are those just loopholes?