I think it's a difficult conversation to have without it being in the Clinic, to be perfectly honest, because that tends to be the main reason. It's less that teams are blacklisted so to speak, and more that teams tended for a long time - at least while there were high profile riders testing positive and issues at major races - to be somewhat risk averse when it came to riders performing at a particular level in scenes or for teams whose reputation wasn't that great, when you could get a comparable level rider out of a more reputable scene or team for the same price. I mean, look at it this way - for a decade, Quinta da Lixa / OFM / Porto / W52 were the dominant force in Portuguese cycling, putting out wattages that would be elite at the WT level in an eleven-day mountainous stage race. Here is the sum total of all the riders that made it to higher levels from their squad:
- Mario Costa, signed to Lampre in 2015 to keep his brother company
- Délio Fernández, spent six years at Delko from 2016-21 and never achieved as much as he did in Portugal
- Eduard Prades, left for Japan in 2014, then earned his way back to Spain with Caja Rural
- Ricardo Vilela, signed for Caja Rural in 2015, spent time with them, Burgos and Manzana-Postobon without success before returning to Portugal
- Joaquim Silva, one year deal with Caja Rural in 2018, returned to Portugal
- Rafael Reis, two year deal with Caja Rural 2017-18, returned to Portugal
- Amaro Antunes, two year deal with CCC 2018-19, returned to Portugal
- José Fernandes, stagiare with EF after only half a season with W52, two years with Burgos, returns to Portugal
So you have eight riders, only two of which made the World Tour (Costa and Prades), only one of which was directly, and even he was only there as a contractual sop to a bigger star. Three signed for Caja Rural (plus Prades after his time in Japan), four of them only lasted one contract overseas, and one of them left in his first season with the team before the stench could get on him.
Barbot / Siper / Efapel / Glassdrive / Sabgal are similar, they've gone through periods of domination, but top tier teams never seem to take a look at their guys. You could argue with Johansen that he wasn't there long enough to get the stench of Portuguese cycling on him, and he had a good record at higher levels before that, so similar to Abner González getting back to Caja Rural (now they're happier to dip their toes back in, after their disaster with Alberto Gallego had them a bit more nervous about it for a while) and James Whelan doing half a season before signing with Q36.5, but it is curious, or would be without the knowledge of the history of the scene there, that nobody ever signed Joni Brandão or Freddy Watts from them. Even when Movistar went to the Volta and saw a 26yo 76kg all-rounder from Uruguay dieseling up the mountainside doing all the things that makes Unzué weep with joy, they didn't offer a contract. Movistar! That tells you something about the perception of the team. André Domingues got onto Burgos, but he has practically no results to speak of before or after Efapel and his single year at Burgos was his last in pro cycling. Before that the last Efapel guy to get to the next level up was when Zé Gonçalves and Diego Rubio signed for Caja Rural in 2016. The last time one of their ex-riders made it to the World Tour before Johansen was de la Parte in 2017 (he rode for them in 2014 and had years at Vorarlberg and CCC before finally getting to the World Tour), and the last one to sign directly to the top tier was Bruno Pires joining Leopard Trek in 2011.
For many years Portuguese cycling was in this position as it paid pretty good salaries relative to neighbouring domestic scenes, but there are also records of certain Italian u23 teams being avoided by certain teams. Sometimes it wasn't necessarily because they were shady, but because they overtrained the espoirs like they were already pro and so those riders had little room for improvement (hello Rabobank development team), whereas somebody getting similar results at another team would still have a lot of potential to increase their performance once competing at the pro level.