This is because of the square-cube-law. Basically, muscle strength is proportional to cross-sectional muscle area, while muscle weight is proportional to volume. So when you take e.g. an insect and start scaling it up, it gets heavier faster than it gets stronger, thus strength relative to weight decreases.
But: I'd seriously doubt that wasps can mine more than an excavator.
Let's take e.g. a Caterpillar 300.9D excavator (weighing 950 kg, same as about a million wasps). That excavator can lift 100+ kg with every swing of the bucket, so if you assume the wasps dig 30x their body weight, the excavator beats the wasps if it can dig more than 300 buckets in one day. That sounds easy - there are 480 minutes in an 8 hour working day, and a bucket each minute is very doable. And on Mars you'd have it fully robotic running 24/7.
Not that it matters, given the way you did the calculation, but it's closer to 10+ million.
but surely we could send 1 boring machine (a small one about 2 meter wide) and bored a shaft straight down, for the first base.
Landing pods on the surface and then covering them in regolith is going to call for heavy machinery. A boring machine is also heavy machinery. These cost an enormous amount to get to Mars. But insect-like robots over a large timescale could do the work at a lower cost.