The thing is, catching dopers is bad for business. Cycling has a bad reputation so catching cheats reinforces that reputation. When big busts happen it's usually been:
a) at times where the faith in the sport has been eroded, such that it is best for business for the sport to display a clear attempt to clean up its act; a lot of the post-Puerto actions, the teams agreeing to pay for the biological passport and so on, fall under this heading;
b) where an athlete is so egregiously obvious in their doping that not busting them would cost the sport reputationally - examples would include Ben Johnson and Johann Mühlegg;
c) where external organisations that do not have a vested interest in the sport involve themselves, such as police-led raids and busts.
Otherwise, it is in the interests of all concerned to let the show go on.
Now, do I believe that everything I'm watching is clean? Hell no. We are seeing 90s-level climbing times and junior-level distance attacks, and riders at opposite ends of the form bell curves, with some riders built like 70s/80s climbers dominating all year and hitting podiums over cobbles, and some riders pushing 40 with physiques that only existed on climbers at the height of the EPO era riding to GT podiums off of the kind of super-peaking calendar the biopassport was supposed to eradicate.
However, why that is the case is where the questions lie. Back in the day there were always a few dopers who would spill the beans on what they did, either to investigations like Emanuele Sella or Jesús Manzano, or in public either at the time like Bernhard Kohl, Patrik Sinkewitz or Thomas Frei, or in retrospect like Michael Rasmussen and Tyler Hamilton. It's been radio silence on that front for a long time even from the few names that have been picked out.
For me, the main questions are:
1) Is there something like "The Clear" or pre-2008 test unveiling CERA in the péloton, are we watching an era that will later be looked back on the way we look at early 90s cycling when EPO was spreading but was not yet known?
2) Are the riders actually taking anything banned, or is there something that is not banned that riders have at their disposal? And if this is the case, then while it's "doping" because that would be "performance enhancing substances", it nevertheless isn't "cheating" - but if it isn't banned, then the question arises as to, should it be, and if so, is that on a physical, health, moral or competition-based justification?
3) Is it just that riders are sticking to a diet of old-fashioned doping techniques like blood doping and already known products, but a number of legal cases have poked huge holes in the efficacy of drug testing, with examples such as Kreuziger, Impey and Froome able to secure exonerations on extremely implausible - but crucially not impossible - justifications, meaning with such a high burden of proof on the tests that actually securing a conviction has become too difficult and/or too expensive to maintain control over the péloton?
4) Is it just that riders are sticking to a diet of old-fashioned doping techniques like blood doping and already known products but with the sport's reputation having been placed in the toilet with controversies hitting several successive champions and having recovered a lot of the lost earnings and audience that that era resulted in, the sport's governing bodies simply don't have the motivation to make those legal battles and will continue to ride the gravy train while the man in the street views the sport less negatively?