Why do so many biochemical reactions require enzymes?
all 10 steps in glycolysis require an enzyme


We count it as 10 steps because there are 10 enzymes. There might be other steps that are fast (like a product acting as an acid or base) that we don't count because they don't need an enzyme.


  I’d have thought that evolution would have selected for “simpler” pathways.


What is simple is that everything is happening in the same reaction vessel, the cytosol (well, there are more compartments, but just a handful). This is different from the organic chemist, who works with very reactive substances in pure form, carefully mixed in separate reaction vessels with distinct solvents refluxed at distinct temperatures for hours.


  Is the very fact that enzymes are required make life more probable since the cells ability to control their quantities make homeostasis and regulation possible?


Yes, that is true. It also allows for a web of reactions rather than a single pathway (you can funnel fructose or galactose into glycolysis, and you can turn pyruvate into lactate instead of decarboxylating it to carbon dioxide and acetic acid).

Stable molecules require catalysts

One requirement for life as we understand it is a way to store, replicate and access genetic information. In our living world, that requirement is met by having nucleic acids. Under physiological conditions, RNA is fairly stable (good enough for a virus) and DNA is very stable (to the degree that sometimes DNA sample from extinct organisms preserve genetic information to this day). If these molecules do not form or decay on their own, there must be enzymes to act on them.

Granted, there could be other pockets of metabolism that work without catalysis. The other requirement, though, is to capture free energy to drive reactions away from equilibrium (e.g. to make the carriers of genetic information mentioned above). This is done through coupled reactions, where e.g. the free energy from food being oxidized (with oxygen as terminal electron acceptor) is captured in proton gradients across membranes and in the phosphorylation of ADP to obtain ATP. If any of the reactions going toward equilibrium would occur without catalysis, the free energy would be lost instead of captured by a coupled enzyme reaction.

General thoughts on complexity

In any complex system (government, computer chip, industrial process etc.), as the complexity grows, the number of steps that seem inefficient or over-complicated will also grow. Many of these steps might not make sense from the present view, but were put in place (or evolved) earlier to meet a historic need. Once in place in a system that has to run continuously, there is often no path to swap it out for a more efficient way of doing things.

One example from biology is the human eye, where the nerve cells run through the optical path, giving rise to the blind spot. The octopus eye "lucked out" and evolved in a way that makes more sense, but human eye sight is just fine (there is a "software patch" in the brain to fill in the blind spot):


Source: https://external-preview.redd.it/xWn0rxCSyu9TrnXozPrsF3aq2_uILbUEJwzBv87TZo4.jpg?auto=webp&amp;s=7a1bccf554ec19a813f9da4466c114ac84c426b7