Waiting for Dropped Riders - Group Ride Etiquette For most casual group rides I've ridden, there are points where the lead pack pauses to wait for dropped riders (usually at the top of climbs).  When the last dropped rider has regrouped, the pack immediately starts off again.  I've always wondered why this is, would not the last rider be the one most in need of rest (especially if it's me!).  If time were an issue, why not just keep going leaving slower riders to go at their own pace?  If concerned about keeping the group together, why not slow down?
There is a lot to unpack on group riding etiquette and waiting for slower riders. Some people ride for social reasons and some people ride mainly for fitness so it can be difficult to balance everyone's need in a large group.

The system we use that I think works quite well is we tend to have about five groups of varying ability and we stagger these groups out over our ride route. The fastest ride is always a drop ride, meaning that no one waits. These are fun but they are intense as it is full on race pace. The idea is if you can't keep up you can always drop down into a slower group that will be arriving in a few minutes. All of the slower groups have a no drop policy. This lets  people filter to their ability and it seems to work quite well as everyone ends up finding their preferred group.

When you only have one or two groups, a no drop policy can cause more friction especially between those that are riding for social reasons versus those that are riding for fitness reasons. Everyone is here to ride, but some have little interest waiting around and socialize they rather do any socializing while on the bike and turning the cranks. For them the act of waiting is already considered a courtesy. They are simply looking to get moving before cooling off too much and are probably not  thinking about how tired the person catching may feel (or forget because they are rested). 

Another  part of it is the HTFU (Harden The F%#@ Up) mentality that has long dominated road cycling culture.  There is the belief that suffering is to be expected and embraced.  As an extension there may also be an expectation that weaker riders should work to improve their fitness and or strategy (e.g., skipping pulls so they can stay rested for a climb) in order to stay better within the group.

As road cycling has been going more mainstream over the last decade or so there have been some growing pains over cultural aspects such as these ones.

Which ever way you slice it it can be difficult to meet everyone's needs especially as the size of groups gets bigger.  The best you can do is looking for a group that best jives with what you want out of cycling. For example, I actually look for rides that drop slower riders (and I have been on the receiving and giving end over the years) because I am specifically out looking for a challenge rather than a social ride.