This is often cited as one of the most famous examples of a rip-off feature. From the characters (especially Mac himself) to the story, to the score, to the visuals, you would have to be blind not to notice it's nothing but E.T. except done worse.

... but what if the director had a different intention than most of us realize?

With a movie like The Room, Ben & Arthur, Birdemic: Shock And Terror, Manos: The Hands Of Fate, even Troll 2, you can tell there's a sincere attempt at making a quality movie. No matter how horrible it turns out.
But Mac & Me is so abundantly goofy and unbelievable that I just don't buy they legitimately wanted to make a good movie. Of course there is also the money angle, but people would have to be really stupid to fall for anything like this.
Life was much more clever in how it ripped off a popular movie, in this case Alien. It presents the story in a new package, with new characters, but it really is like watching a straightup remake. It was honestly kinda annoying how shameless it was about trying to recreate the magic while also pretending to do their own thing. However, because it's so neatly presented, it's easier to lure people into buying tickets. Even those who recognize all the familiar elements will still go for it.

So if Mac & Me isn't trying to be a quality product nor just trying to make money, what is it attempting in that case?
I think it's a parody in disguise.

The E.T. monster while well-designed, looks hideously ugly, so of course they make him even uglier and weirder-looking. The Reese's Pieces product placement is a very remembered aspect of the movie, so they go the extra mile and advertise McDonald's and Coca-Cola, even making it a part of the plot. It also imitates classic sequences, but puts a bizarre twist on them, such as the bike scene from the original getting transformed into Paul Rudd chasing Mac with a wheelchair. And instead of just hitting the brakes, he falls into a lake!
There's also stuff which wasn't in the original, but just were put in there for the hell of it, such as the explosion near the mall and the alien creatures attending church. Spoofs often come up with wacky scenes of their own as well.
Finally, the dialogue is completely over-the-top and impossible to take seriously. It's not just unintentionally funny, there are lines which were clearly meant to be funny on purpose:

Eric Cruise: [spinning a flower in a soda can straw] Maybe these are just flowers?
Courtney: How about a spaceship?
Debbie: Great.
Michael Cruise: Yeah, and then we have a close encounter of the third kind.

Michael Cruise: You know what I feel like?
Eric Cruise: A Big Mac?
Michael Cruise: The man's psychic!

The more I consider this theory, the more it makes sense to me.
__________________