Like everything else, the ascent and descent stages were built to be as light as possible. But because they knew they would operate only in a vacuum, many things really didn't need to be sturdy, nor did the shape of it matter. It would never have to deal with aerodynamic drag. In fact, the descent stage was designed to buckle in the right places upon landing, that was how it absorbed the impact. It was only going to be used once, this was the most weight-efficient method of handling the shock of landing.
Also, the complex insulation blankets covering the module had many layers, and contact points between the layers needed to be minimized so that heat wouldn't be passed through them by conduction. The black material is where thin Inconel sheets formed the outer layer of the insulation blanket, and they were painted matte black with Pyromark paint to improve their heat emission properties, so they would cool off quickly. (Black material both absorbs and emits heat better than material of other colors.) Beneath the black layer were reflective layers to prevent the heat of the black layer penetrating into the module. This treatment was done where the exhaust of the reaction control thrusters heated the lunar modules. It had a tendency to crinkle, and on this particular module, that may have been accentuated by the fact it was in fact installed at the last minute, as were the chutes under the thrusters. From the Lunar Module Coatings Page:
A few months before flight, shock tunnel tests using a new thruster
duty cycle revealed that the Pyromark painted Inconel lay-ups on the
upper sides of the Descent Stage quads would not be sufficient
protection against the hot plumes. A crash program to design a fix
resulted in "coal chute" plume deflectors mounted below the
down-firing jets. These were installed on LM 5 while it was on the
pad, just before launch.
Another last minute thermal fix added 39 pounds of Kapton and Pyromark painted Inconel to the landing gear, pads and probe. One
of the reasons for this added weight was a crew request(!) that they
be allowed to keep the engine on past probe contact to pad touchdown.
This would result in greater heating from the engine plume as it
reflected off the lunar surface past the gear.
Considering the vast ambition of going to the Moon for the first time, it isn't surprising some fixes were last-minute.
The foil is Kapton MLI (multi-layer insulation) blankets, and it is actually pretty complex. In the places on the lunar modules that only needed to be a heat barrier to sunlight, high reflectivity was the most efffective approach, and those places are the shiny amber color of the Kapton. As there is no air in space to pass heat by convection, if you lower absorption of heat radiation by making surfaces that are highly reflective or emissive, and there are few contact points to pass heat by conduction, insulation can be highly effective. With the Kapton foil blankets, the contact points were reduced by hand-crinkling an inner layer of the blanket. From the Apollo News Reference:
To make an even more effective insulation, the polymide sheets are
hand crinkled before blanket fabrication. This crinkling provides a
path for venting, and minimizes contact conductance between the
layers.
So, this is bound to make the outer layer rather uneven.
All the other covering material you see is also just there to protect whatever is underneath from the effects of sunlight. Perhaps they were also thinking a bit about keeping dust out. That is all it has to do, and it was made merely sufficient for that job.
Weight savings were more important than looks. The fancy stuff is underneath all those bare-bones panels.
I found a different photo of the lander that gives a better sense of the complexity of it. The photo shows the Ascent Stage in the process of assembly, before the heat shielding had been put on it:
This photo of an LM test article shows the sturdy underlying aluminum and titanium structure pretty clearly:
And a quote from the book Chariots of Apollo available on the NASA website's History section:
By the end of 1965, Scrape and SWIP had pruned away 1,100 kilograms,
providing a comfortable margin below the control weight limit. One of
the more striking changes to come from this drive for a lighter
spacecraft was the substitution of aluminum-mylar foil thermal
blankets for rigid heatshields. The gold wrapping characteristic of
the lander's exterior saved 50 kilograms.
Many of these weight-reducing changes made the lander so difficult to
fabricate, so fragile and vulnerable to damage, that it demanded great
care and skill by assembly and checkout technicians. Structural
components took on strange and complex shapes, requiring careful
machining to remove any excess metal
'Scrape' and 'SWIP' were both programs Grumman, the company that fabricated the Lunar Module, instituted specifically to reduce the weight of the LM.
I found both things on a great thread on the topic at CosmoQuest
You can pore over the LM Apollo Operations Handbook for a great deal of technical information on the spacecraft, for more evidence.
