ESD ratings of diodes and bipolar transistors
ICs are ESD protected by connecting diodes from I/O to rails.

How would you protect a diode? By using another diode? The diode has two possibilities when hit with an overload. (a) It conducts in the forward direction. Many diodes have a peak current specification, which tends to be orders of magnitude higher than the sort of diodes you can fit into an IC for protection. (b) It blocks in the reverse direction. You already have a specification for the peak reverse voltage it can take without breaking down.

Transistors are similar. If you hit a junction in reverse with an ESD spike, you already have in the data sheet the voltage limit for that junction, above which it may break down. A forward junction will tend to protect itself as for a diode.

Generally, the common 'cooking grade' transistors (like BC847) are fairly robust, built with big processes. It's ICs with small junctions that need explicit protection, and FETs with a very high impedance gate. You can buy microwave diodes and transistors that are very susceptible to ESD, as they have to be built with tiny junctions to work at high frequency.