@Daniel_Y there are at least two straight tubes on my bikes! 
I’m not as crazy as Blacksheep and Oddity though, they’re next level.
Oakes Mfg next door to Blacksheep in Ft Collins used to make the clamshell dies for a 2-ton HF hydraulic press and cost was about $1100 just for the dies. They were used for those dual bend down tubes or a kinked top tube klunker, and seat tubes. It’s not as easy as clamping the tube and squishing it though. Bending is a dark art that only some have the patience and cash to dive into completely. One wastes a lot of tubes learning what works and doesn’t. You need a variety of benders and dies for each part of the bike although the Cobra is extremely useful for seatstays, chainstays, seat tubes, even kinked top tubes, but you’ll need all those dies. No other bender can do that unless you have a Diacro and the knowledge of how to machine dies for it.
Anvil sold a bender I still use mostly for handlebars. The reason Blacksheep and Oddity and Myth and others have made their own benders is because nothing has the side clearance for riser bars. If you look closely at the videos people have done coming out of those shops you may be able to catch a glance at their setups but they tend to keep their designs out of the photos since it lets them do what they do. James is probably the most likely to share his setups.
Below is the Oakes one but their bike site is down, I think they got too busy during Covid and stopped making bike bits.
