What happened with Chronicles?
The difference is that wizards printed a whole lot of chronicles, and they sold it cheaper than normal packs.  

The result was a massive market flood of cards, some of which actually were somewhat valuable. compare the prices of  Nicol Bolas to other obscure legends that weren't printed in chronicles like Angus Mackenzie, to see how chronicles affected it.  

The value of people's collections dropped drastically, and people don't like it when that happens.

Modern masters was different because wizards charged more for them and they purposefully printed a very limited run of it.  

if you wanted to get modern masters for MSRP, you had to already know that it was coming.  Stores that sold them at MSRP sold out in less than a day.