Why not take insulin orally (pills)?

A couple companies are working on this.

• There are several hurdles associated with delivering insulin orally. They include the highly-acidic nature of gastric liquids, the complex nature of the insulin molecules, the rate at which epithelial cells absorb the compound and so on. In order to circumvent most of these problems, the Novo team turned to protein engineering, so as to modify insulin according to needs. “You can't use human insulin [for developing orally-delivered pills]. ]It doesn't work,” explains Novo's chief scientific officer, Mads Krogsgaard Thomsen. The team is currently still tweaking its final product, details of which are currently kept under wraps. Softpedia

• Chemists from the the Topichev Institute for Petrochemical Synthesis have suggested a unique and efficient solution to the problem having split it into two parts. To ensure that the remedy gets into the blood out of the pill, it is required that the remedy slipped `safely` through the stomach - this is stage one. Then it is necessary to make sure that the remedy gets into the blood in the small intestines quicker than the enzymes would destroy it - this is stage two. Innovations report

That second quote was from eight years ago so I am guessing their clinical trials presented some serious problems.