There are plenty of animals that don't suffer the same was a chimps to, such as mice, that can be used for a lot of the tests.
The argument is that while chimps are convenient test subjects, there are alternatives. More expensive alternatives, but we should at least think about what price we are willing to put on the suffering of highly developed animals.
My guess is that there are very few drugs tested on chimps that aren't first tested on mice. They aren't using chimps because it is cheaper.
Chimps are A LOT more expensive to do testing on than mice. Not to mention if there is a adverse reaction and the chimp dies then you have
the significant cost of both time and money getting a new chimp where mice cost next to nothing and are easy to obtain. I doubt you can
find me a single drug that was tested on chimps before it was tested on mice. Chimps are generally the last leg before it goes to human trial.
Yes, we might be able to skip that last leg but if the chimp is treated well, I think it's better to test on a chimp than on someone's 6 year old kid.
The other option of course is the prey on the poor and offer money for people to volunteer as test dummies. I think doing final testing on chimps
who are well cared for is the best option we have.