Not only does he still have a memorial for Robin set up in The Batcave (placed there after Harley Quinn and Joker killed him before the events of Suicide Squad), but Justice League also shows us that he keeps Joe Chill’s pistol (the one that killed his parents) encased in glass.
This idea certainly makes quite a bit of sense when we consider just how sentimental Bruce Wayne is in the DCEU.
If Robin did ride a motorcycle during their partnership, then it would seem in-character for Bruce to keep it in the cave to collect dust.