There are essentially zero kids "available" to adopt outside of foster care. And foster care is (correctly imo) focused on reuniting children with their parents when possible, so the typical case of adoption being possible is when the parents are truly unsafe.

In our experience meeting other foster parents at trainings and such, around half were fostering with the goal of adoption.

Fostering can definitely lead to adoption (and in particular there is a need for parents willing to adopt teenagers) but it can be a long process with no guarantees. On the other hand, it's much cheaper than other paths to adoption, either domestic or international.

In our case we are open to adopting (and the more kids we foster, the more likely it is that we end up in a situation where adoption is on the table) but we are mainly fostering because we know there are kids out there right now that need parents, even if just for a few weeks, months or years.

You can't adopt the kids if the parents still have a chance to get them back. That either ends via legal action by the state, or voluntarily giving up rights. This often happens when parents go to prison, for instance, since there's no chance of them caring for their kids. You also have to exhaust all relative chances first as well before they can be adopted (Indiana), so this can take 1-3+ years. In English, there's a need for kids to go somewhere that can't be adopted yet, and around half go back to mom and dad or family anyway. We had one kid for three days, and two for six weeks, so not every kid is years long anyway.