Why does SOT89-ECB footprint exist?
... a part that has a footprint SOT89-ECB (PNP-BJT), ended up on my board, but when I tried to find a transistor that actually has compatible pin configuration I came out with nothing. So what is the point of even having a footprint like that in a standard library ... Are there actually compatible parts that I did not find?

The footprint may be useful for an XC6372 - your brain may need a second or two to recalibrate when 1st looking at that page :-).
The BCX53 has the base on the left, emitter on the right when viewed from on top , leads towards you. This is the industry standard SOT89 bipolar pinout. = BCE.
Data sheets like this one may mislead you - until it is realised that they have (stupidly) shown a bottom view. SOME sellers advertise this as ECB pinout  eg this page shows it as ECB - but they are wrong.
&quot;BEC&quot; !!!-  SXA289 - admittedly for good reason :-).
The fact that the &quot;strange&quot; BEC configuration exists for the SXA289 (see above) MAY provide an answer. The 289 is designed as a stripline RF amplifier with central emitter grounded and signal passing symmetrically across the component - hence BEC. It could equally have been CEB.
It is conceivable that in some niche circuits it is advantageous for complementary parts to have either bases or emitters physically adjacent. So a ECB-BCE or BCE-ECB arrangement might then make sense.
Using FETs rather than bipolars a contrived example is two FETs of the SAME type but with opposite pinout being arranged adjacently to provide a GDS-SDG arrangement (equivalent to bipolar BCE-ECB) with sources joined AND gates joined. You now have a back to back/series opposed pair that acts as a bidirectional switch when Vgs is applied to turn on both transistors at one (each operating in different quadrants!).