Fission is Easy
Natural fission reactors exist on earth, at a small scale, and low energy. However, the smallest natural fusion reactor is probably the brown dwarf, which has a mass at least 10x Jupiter's. If we compare the masses of these natural reactors, it's clear that fission is at least 6 orders of magnitude easier than fusion (and probably closer to 9-12...just too lazy to do the math).
As others have pointed out, the only reason fusion bombs even exist is because we can use fission reactions to compress the fusion products. If fission bombs weren't practical, we would almost certainly not have any fusion weapons of any kind right now.
Fusion is Hard
You should be glad that fusion is hard. If it were easy, then a lot of elements would not be stable. Imagine if a car crash concentrated enough energy to transmute elements. Even a rocket launch might permanently change the exhaust products. Chemistry itself would become relatively unstable.
Unfortunately, the flip side is that to achieve fusion, you need to inject a lot of energy into a fairly small space. If you don't have 10 Jupiters of gravity to do that work for you, then the energy needs to come from somewhere else: lasers, plasma, really powerful hammers, etc. And since the fusion targets tend to be very small, it is extremely difficult to get all that input energy to drive fusion, rather than just heating up your target. This is what Mr. Doty is referring to with the square/cube scaling.
Simply heating up a fuel pellet to 1 million degrees isn't very useful. It's really an enormous waste of energy. If we could get all that energy to turn into fusion reactions, we would be golden. In reality, only a fraction of that turns into fusion reactions, so we don't get a whole lot of fusion out of each attempt.
Fusion reactors require a tremendous amount of energy just to operate. If they could produce more energy than they consume, then once started, they would be self-sustaining. But as others have noted, sustaining a fusion reaction is even harder than starting one.
ITER, one of the oldest and most mature fusion reactors, takes about half a gigawatt to operate. That's roughly a medium-sized power plant that could normally power a decent-sized city, just to warm up a single fusion reactor.
NIF, which uses lasers to trigger fusion, only converts about 10% of the laser energy into potential fusion. That's not even taking into account the thermal losses in the lasers themselves, which are some of the most powerful ever built, or all the energy spent running cooling pumps and other essential equipment.
Fission is efficient at human scale, but uncontrollable at planetary scale (if you had a fissile pile the size of a planet, good luck making a power plant out of that). Fusion is relatively efficient at stellar scale, but extremely difficult at human scale. The reasons have to do with the relative strength of the electromagnetic, strong, weak, and gravitational forces.
Note that thermonuclear weapons are not called "fusion bombs" because fusion is just one component of the total design. Multiple fission reactions occur and are necessary to the total effect, including fission of the fusion fuel itself! As much as half the yield of these weapons comes not from fusion, but from fission processes. The destructive power comes not from fission or fusion alone, but from fission triggering fusion, and then fusion triggering more fission.
And a bomb is always easier to design than a power plant, because no containment or energy harvesting is needed. The lack of containment is a feature for a bomb, and a massive liability for a power plant. It's just a lucky coincidence that fission is calm at small scales and explosive at larger ones, while fusion is, in some sense, the opposite (meaning, gravity-driven fusion is relatively "calm" and stable, while plasma/ICF is pretty unstable).