I don't get how the 135L can be so cheap and the 35L so expensive?
It is the difference in designs. A 35mm lens on a 44mm flange distance is a retrofocus design, that is it has to bend the light multiple times to get it to focus on the sensor, telephoto lenses, in contrast, are very simple lenses to design and build, it is a straight shot through to the sensor and additional elements are just for correcting aberrations.
The TS-E 17mm was the lens that made me realise all Canon lenses are exactly as designed, and the compromises in them are there for specific reasons, cost, quality tradeoffs, etc. Look at the 70-200 f2.8 IS MkII compared to the MkI, sports shooters love it because it is sharper and focuses faster, meanwhile portrait shooters are not so keen because of the slightly harsher bokeh, all trade offs, but all built in at the design stage. Anybody that can make a 17 mm lens with zero distortion is very clever, anybody that can make a 17mm lens to work on a 44mm registry distance is comfortably smarter than that, but to then drive home the total dominance of lens design and build capability by making it a tilt shift lens is, quite simple, showing off.
Canon make the lenses they do for marketing reasons, they come with the limitations and characteristics they do to meet the brief for that lens. It seems the brief can be top quality at any cost and we will sell them for what we can get, the prestige thing, like the 17TS-E and the 200 f1.8, it was said that Canon made a loss on every 200 f1.8 they sold; or the brief can be how cheap can we make it to get people into a system, the 50 f1.8 and many kit zooms spring to mind.
Another consideration is that the needs of film and digital sensors is quite different, most of these lenses core layouts were designed long before digital and the need for perpendicular, or as close as possible, light rays, another major consideration for wide angle and retrofcus designs. Certainly any new wide angle designs will take that into consideration.