Why is not Bech32 address selected as default in Bitcoin Core 0.16.0? So, thankfully Bitcoin Core 0.16.0 came to us, general people.

But however, native segwit address Bech32 wasn't selected as default.

Is not it better to use a Bech32 address right away rather than P2SH segwit-wrapped address?
Bech32 Addresses is still not supported on the other platforms. There are many libraries even considering bech32 address as "invalid." 

If I'm using Bech32 address and asking someone who is using another platform to send me some bitcoin they may never be able to make the payment. 

We need some time so it becomes supported everywhere.

Right now Blockchain.info, Electrum doesn't support bech32 address and they're highly used.