Unlimited stack size with pthreads

My default stack size (according to ulimit -s) is 8192 kB, so naturally the code below segfaults when I try to run it. Also, naturally, it works fine if I do a 'ulimit -s 9000'. However, when I do a 'ulimit -s unlimited' the code segfaults again. Any ideas what is going on here? If it's useful, I'm running Debian 10 with kernel 4.19.0-6 and gcc version Debian 8.3.0-6.

#include 
#include 
#include 

void* wait_exit(void*)
{
  char bob[8193*1024];
  return 0;
}

int main()
{
  pthread_t t_exit;
  int ret;
  
  if((ret = pthread_create(&t_exit,NULL,wait_exit,NULL)) !=0)
  {
    std::cout<<"Cannot create exit thread: "<