I don't think it's particularly weird, it's about misrepresentation. Most users attracted to open source licensing aren't aiming for abstract goals like "give away a lot" or even "give away as much as possible", they're aiming for "give away practically everything so they can use it for free in any way they want". Proprietary products don't waste these users time as they are clearly not suitable, but advertising an open core product as open source will attract a lot of unsuitable users who desire open source when you're offering open core.

If you're trying to make money, just don't do open source. No one owes you kudos for striking a compromise no one wants.