I still think attending comes down to simple good manners, like most things. If you are invited, you may attend; politely and respectfully, taking care not to overstay your welcome.
Your original discomfort can only be understood as being aimed at the hosts, for inviting people whose suitability as participants you are questioning. Why would the hosts do that?
And indeed, you tell us you believe the hosts must be proselytizing.
Because in your experience, of one sub-genre of one religion, that is the only reason all and any people of faith invite anyone to any celebration. (You've slipped up here by equating events in church buildings with Eid celebrations in people's homes, parks and community centres).
Maybe there's a lesson in neighbourliness, friendliness and community spirit in this for you?
Incidentally, in my area, there has been at least one very large, new, Christian church built in the last 10-15 years, to accommodate a thriving evangelical congregation. That's not a depletion in Christian congregations, it is a shift in the style of worship and demographic composition of the congregation.