I was kinda curious for myself, but also just in general, so I went through and figured out what all episodes are currently missing from streaming on Max (as of today - this may change, given how we lost entire seasons for a while a few months back). I can't seem to find any connection on how or why these are all missing at first glance compared to others.

I compared what was listed on Max next to the List of MythBusters Episodes page on Wikipedia. I broke down by each annual season (using that page) and what the equivalent episodes are in Max. Note that episodes are not always in the same order, but I'm listing what's missing and accounting for that as best I can.

Pilot Season

• Episodes Available:
• JATO through Poppy Seed Drug Test (Season 1)
• No episodes missing

2003 Season

• Episodes Available:
• Exploding Toilet through Alcatraz Escape (Season 2)
• No episodes missing

2004 Season

• Episodes Available:
• Explosive Decompression through Buried in Concrete (Season 2)
• Myths Revisited through Ming Dynasty Astronaut (Season 3)
• Christmas Special (Season 101)
• No episodes missing

2005 Season

• Episodes Available:
• Buster Special and Ultimate MythBusters (Season 101)
• Brown Note through MythBusters Revealed (Season 3)
• Confederate Rocket through Sea Sickness Cure (Season 4)
• Missing Episodes:
• MythBusters Outtakes
• Jaws Special
• Vodka Myths

2006 Season

• Episodes Available:
• Paper Crossbow through 22,000 Foot Fall (Season 4)
• Holiday Special (Season 5)
• Missing Episodes:
• Archimedes Death Ray Revisit
• Cell Phones on Planes
• Bullets Fired Up
• Myths Re-Opened
• Crimes and Myth-Demeanors 1
• Steam Cannon, Mentos and Soda
• Mega Movie Myths

2007 Season

• Episodes Available:
• Hindenburg Disaster through Airplane Hour (Season 5)
• Missing Episodes:
• Grenades and Guts
• Baseball Myths
• Special Supersized Myths

2008 Season

• Episodes Available:
• James Bond Part 1 through MacGyver Myths (Season 5)
• Alaska Special through Viewer Special Threequel (Season 6)
• Missing Episodes:
• Shark Week Special 2

2009 Season

• Episodes Available:
• Alaska Special 2 through Mini Myth Mayhem (Season 7)
• Missing Episodes:
• Demolition Derby

2010 Season

• Episodes Available:
• Boomerang Bullet (Season 7)
• Soda Cup Killer through Top 25 MythBusters Moments (Season 8)
• Tablecloth Chaos through President's Challenge (Season 9)
• Missing Episodes:
• Hair of the Dog
• Storm Chasing Myths
• Cold Feet
• Arrow Machine Gun
• Inverted Underwater Car
• Green Hornet Special
• Operation: Valkyrie

2011 Season

• Episodes Available:
• Blue Ice through Paper Armor (Season 10)
• Bikes and Bazookas through Toilet Bomb (Season 11)
• Missing Episodes:
• Mission Impossible Mask
• Running On Water
• Planes, Trains, and Automobiles

2012 Season

• Episodes Available:
• Duct Tape Island through Hollywood Gunslingers (Season 12)
• Titanic Survival through Explosions: A to Z (Season 13)
• Missing Episodes:
• Jawsome Shark Special

2013 Season

• Episodes Available:
• Deadliest Catch Crab-Tastic Special through Zombie Special (Season 14)
• Missing Episodes:
• JATO 3: Mission Accomplished?

2014 Season

• Episodes Available:
• Star Wars: Revenge of the Myth through Supersonic Ping-Pong Ball (Season 15)
• Fire In The Hole through Plane Boarding (Season 16)
• Missing Episodes:
• Commercial Myths

2015 Season

• Episodes Available:
• Simpsons Special through San Francisco Drift (Season 17)
• Blow It Out of the Water through Star Wars: The Myths Strike Back (Season 18)
• No episodes missing

2016 Season

• Episodes Available:
• MythBusters Revealed: Season Opener Special through Duct Tape: The Return (Season 19)
• No episodes missing

In total that's 28 episodes currently missing, including some fairly major ones like Bullets Fired Up (Adam's talked about how that's contributed to actual academic studies on bullets) and both Special Supersized Myths and JATO 3: Mission Accomplished? (the two revisits of the original JATO myth), the first Archimedes Death Ray revisit episode, among plenty of others.