FPGAs are still quite common in niche hardware like oscilloscopes or cell towers, where the manufacturer needs some sophisticated hardware capabilities but isn't manufacturing enough units to make the NRE for an ASIC worthwhile.
Eventually Nokia ended up buying Alcatel Lucent and not too long after he left, not sure what their current strategy is.
For some workloads, an FPGA is orders of magnitude faster than a CPU.
All the modulation, demodulation, framing, scrambling, forward error correction coding/decoding, etc. has to all happen continuously at the same time.
There are some open source software defined radios that can do that for one or two stations on a CPU at low data rates, but it's basically impossible with current CPUs for anything like the number of stations (phones) that are handled in one FPGA with decent data rates, latency etc.
You'd probably need a server rack's worth of servers and hundreds of times the power consumption to do what's happening in the one chip.