I've seen a few Kaiju stories, and other than Pacific Rim 2 (ugh), I don't think they explain why Kaiju end up in big cities (correct me if I'm wrong). You'd think that the buildings would make manoeuvrability hard and cause them lots of injuries, so it'd be really inefficient. How do I make my Kaiju believably go to a city?
First, out of world motivation is rule of cool.
Try rephrasing the question "If a tree falls in a forest and no one is around to hear it, does it make a sound? to "If a kaiju walks in a place and no one is around to hear it, does it make a sound?"
A story where your kaiju would attack a barren land wouldn't be as interesting as if the target is a large city.
Second, in world explanation is that big cities, with their large footprint in term of emitted sounds, lights, smells and food are not meant to stay hidden for a creature which is a top predator.
Reputation. Being a kaiju is a cutthroat field. Nobody wants to be yesterday's monster, only fit for D-list heroes to cut their teeth on. You want to be the top, the biggest, baddest, most impressive monster around!
And that means picking big fights that really matter. Let's be honest, if you had two monsters, one wrecking Tokyo and the other trampling Des Moines, Iowa, which one would you pay attention to? Probably not the one menacing your cornfields.
reproduction or energy
Kaiju are unbelievable themselves. Their size and weight is impractical from the start. Their own weight threatens to crush them. They have a relatively low surface area which endangers to overheat them as they can't dissipate heat. Their lungs, heart(s) and veins need to work so incredibly hard they will wear out fast. Their food intake would be incredibly difficult. This means one more unbelievable thing might not be noticed as much.
Ignoring these problems, the cities have several things in abundance. Certain materials in buildings, garbage, humans and energy in the form of electricity and oil. Each can be a reason to stay there.
The building (materials) can be used as shelter or a nest (premise of one of the Godzilla movies for the observant). Only tall jungles and buildings will likely hide such big creatures, which is a desire of many creatures for sleep or reproduction.
The humans might seem as a nice addition to their normal food. There is a huge concentration of them in the cities. However, a kaiju would need to eat a lot of humans to stay alive. If it reproduces, the children can prey on the humans.
Finally the energy. For whatever reason, electricity or oil can help the creature survive (or undergo metamorphosis. New Godzilla movie). Maybe an addition to food intake. There is an abundance of electricity and oil in cities.
To get rid of skin parasites
Years ago, I saw a nature documentary where a bird was attacking an ant nest. The ants were trying to defend themselves by spraying the bird with their formic acid. It was then explained that the bird had no interest in eating the ants, and that their formic acid had no effect on the bird... but it was lethal for the bird's skin parasites, which was the reason why the bird was assaulting the anthill.
Kaijus are usually big t-rex-like creatures, which means that their tiny arms aren't the best tool to scratch or to remove parasites, so they need to find an alternative method.
For a kaiju, attacking a city is the best way to upset a lot of those small creatures, which start to attack him with rifles, tanks, cannons and so on... These weapons have no effect on the thick skin of the monster, but are extremely effective in killing all of the (huge) fleas and ticks that torment the poor kaiju.
As a bonus, the concrete buildings, being tall and rough, are extremely good also for scratching the back, like the trees for the bears
Kaiju were not always so big.
Big grazers like it out in the open, so they can see what is coming. But lots of other animals like things around them. Especially smaller land animals like cover - down in the rocks or underbrush, hidden in the surroundings. An animal suddenly out in the open will run for cover and hunker down.
Your kaiju have brains that are for smaller animals. Some force made the kaiju big. Now too big for their worlds, they feel exposed towering above everything, the wind blowing on their skin, eyes staring at their exposed bigness.
Being in with the big buildings feels right to certain ancestral parts of their brain. They like solid stuff around them providing cover. Outside of cities, it is hard to find natural formations that provide a comparable environment.