Probably this feature wasn't used very often, but a small percentage of Gmail users will miss it, especially business users. Adding invitations from Gmail is more convenient than opening Google Calendar in a new tab, creating a new event and inviting guests.
"It (truly!) is always tough choosing which features to continue to support. We make these decisions carefully, so please know that! We'll still be supporting creating invitations, just through different steps. The workaround now is to click into calendar and to create an invitation from there," inform Gmail Community Managers.
{ Thanks, James Sacuan. }
