From both a hardware and software perspective those are very different types of parallelism that Nvidia's architects and the architects of its predecessors at Sun/SGI/Cray/elsewhere were intimately familiar with. See: https://en.wikipedia.org/wiki/Flynn%27s_taxonomy
A bunch of threads in parallel implies MIMD parallelism- multiple instructions multiple data.
A warp implies SIMD parallelism - single instruction multiple data (although technically SIMT, single instructions multiple threads https://en.wikipedia.org/wiki/Single_instruction,_multiple_t...).
From both a hardware and software perspective those are very different types of parallelism that Nvidia's architects and the architects of its predecessors at Sun/SGI/Cray/elsewhere were intimately familiar with. See: https://en.wikipedia.org/wiki/Flynn%27s_taxonomy