Cuz 8 GB max in 2017 is lame, even for a MacBook. OTOH, 16 GB for a MacBook will cover 98% of the MacBook buyer population. Yes, I made that number up, but you get the gist of the what I'm saying. Considerably more MacBook Pro users would benefit from greater than 16 GB.
The way I see this shaking out in 2018 is something like this:
12" MacBook
Dual-core fanless
16 GB max RAM
512 GB max SSD
13" MacBook
??? Dual-core (or ARM) fanless
16 GB RAM
512 GB max SSD
13" MacBook Pro
Quad-core
16 GB max RAM
1 TB max SSD
15" MacBook Pro
Hex-core
16 GB max RAM
2 TB max SSD
The way I see it in 2019 is something like this:
12" MacBook
Quad-core fanless
16 GB max RAM
1 TB max SSD
13" MacBook
??? Quad-core (or ARM) fanless
16 GB RAM
1 TB max SSD
13" MacBook Pro
Quad-core
32 GB max RAM
2TB max SSD
15" MacBook Pro
Hex-core
32 GB max RAM
2 TB max SSD
All bets are off for 2020.
Should be 32GB for MBP:
https://ark.intel.com/products/136863/Intel-Core-i3-8121U-Processor-4M-Cache-up-to-3_20-GHz