Commercial farming of those vegetables, at the least in certain areas of the world, often involves migratory beekeeping. In places such as California, you can find not enough local bees or any other pollinating insects to pollinate the huge almond orchards. Bee hives are transported regarding the back of large trucks between farms — they might go from almond orchards in one part of the US then on to avocado orchards an additional, and soon after to sunflower fields over time for summer.
Vegans avoid animal products. For strict vegans what this means is avoiding honey because of the exploitation of bees. That appears to imply that vegans also needs to avoid vegetables like avocados that involve exploiting bees inside their production.
The revelation that avocados may possibly not be “vegan-friendly” could seem to be a reductio ad absurdum for the ethical vegan argument. Some people might point out this and declare that those who are vegan but still consume avocados (or almonds and the like) are hypocrites. Alternatively, this sort of news might lead some individuals to throw up their hands in the impossibility of living a really vegan diet, and thus to stop.
However, one initial defence for vegans is the fact that this might be only a problem for several vegetables which are produced commercially on a big scale and that are determined by migratory beekeeping. In places for instance the UK, this practice continues to be uncommon. Locally sourced butternut squash would probably be fine (although you could never guarantee a bee kept in a hive had not pollinated a crop), while avocados and almonds (including most almond milk) sourced from California could be a challenge.
Another answer might depend on someone’s view about the moral status of insects. Commercial beekeeping may injure or kill bees. Transporting bees to pollinate crops seems to negatively affect their own health and lifespan. But some may question whether bees are capable of suffering in the same manner as animals, while some may wonder whether bees are self-aware — whether they have a desire to carry on to reside. When they do not, some philosophers argue that they would not be harmed by being killed.