Many people respond better in group settings. Bonding is a great motivator for some.
FWIW, I do subscribe to the idea that you 'never lose your rank' but when there has been a long break it is oftentimes easier/better on everyone involved to just start back at the beginning until thinks start gel again. IMHO, there is few things worse than a training environment where there are several high ranking people who just cannot or do no know the curriculum. Much better to be belted accordingly. One Huge advantage is removing the imposter syndrome phobia.
I have had many people start back after longs breaks over the years. After talking it through and having a good understanding where they are relative to their break and what, it any training they have been doing, I always give them the option of keeping their belt or starting over (or at a lower belt). I would say about 60% start over/lower belt and skip test if/when appropriate.