Why did early humans begin to walk on two feet?

Why did early humans begin walking on 2 feet?
Some say they needed they need to walk on feet in order to bring food to their lovers. Being bipedal would definitely have helped/ made doing this more productive because, you can carry more food if you have two hands to carry food with (if walking on 4 legs could only carry small amount of food in your mouth.) Another theory that was explored by scientists is that early hominids needed bipedality in order to walk across the hot savannas. And how could bipedlity have helped that? Well, seeing has the forests had started shrinking and the hot savannas had started expanding, hominids needed a way to cross the savanna's in order to reach the cool forests. And being bipedal would help do this because walking is a faster mode of transportation and also the grasses we tall and you needed your full height to see over them. Walking upright through the burning savanna's brings me to the next theory; that being bipedal saved energy, and it was a more efficient mode of transportation. This is because scientists said that walking/running on 2 feet saved more energy and was faster because standing upright expands your lungs making breathing easier making it easier to go longer distance's. However after preforming several experiments this theory was eventually discharged. The last theory is that early hominids started walking upright in order to pick up and start using tools, bipedality definitely would have helped the use and development of tools. Because, while hunting having to hands made carrying tool much easier also, hominids became more skilled with their hands which helped creating more complex tools.
To conclude, the theory that I find most plausible is that hominids became bipedal in order to cross the heating savanna's however no theories have been proven correct and scientists have no idea the reason humans became bipedal. However every theory seems to be interlinked which is probably one reason discovering the root of humans bipedalism has proved to be so challenging.