More than 16GB RAM isn’t as simple as you’d think. DDR3 has a limit of 16GB RAM. To go higher, you need to switch to DDR4. Intel mobile chipsets do support DDR4, but they *do not* support Low Power DDR4. A switch to DDR4 to allow for > 16GB RAM would have a significant impact on battery life.
“So just add more battery!”
Also not so simple. The FAA limits laptop battery size to under 100 watt-hours. The MBP battery is already at 99.5 watt-hours. Apple literally cannot put more battery in the thing without it being banned from airplanes. This is something all laptop manufacturers must deal with.
Suddenly, many inexplicable design decisions make a ton of sense when you consider that battery life is a priority for Apple. The RAM limitations, the slower GPU, etc. Everything is a balancing act with battery life. It all impacts portability.