I am not sure what you are basing this one. That might be true in your experience, but patently is not true in the Oxford magistrates court. In the
summary page I found at random, 32 cases reported. 28 had fines of £100 or lower regardless of plea. There are only two of the same magnitude as the cyclist got and there is also bizarrely precise costs of £382.75.
Apparently this takes the same sort of legal effort as putting together a charge of cycling on the pavement:
MOHAMMED AZAM, 39, of Easington Road, Banbury, was convicted of assault by beating a woman in Banbury on August 8, breaching a restraining order in Banbury on August 12, assault by beating a two people and driving without insurance, taking a vehicle without consent, breaching a restraining order and damaging a £200 iPhone in Banbury on August 26. Jailed for 18 weeks. Restraining order made preventing defendant from contact with certain people and locations. Victim surcharge £115, compensation £150 and costs £725. Six penalty points.
Unless you sit in the court, you really cannot draw conclusions.
Standard prosecution costs for a plea of guilty is £85.
Trials are a bit more complex.
in the case of Azam, he was ordered to pay compensation which the magistrates often prioritise - it is also taken first where the defendant pays weekly from benefits.
Thus the costs application for Azzam might have been higher, but the bench reduced it a bit in favour of compo - victim first and all that.
Magistrates sometimes make no order for costs even on a guilty plea if the defendant is absolutely potless and the offence is very minor.
Same thing can happen with guilty pleas to minor shop thefts - compo of the value of whatever was taken, but no costs.
As with most things in the courts, we always do it one way except on the occasions when we do it another way.
Top and bottom of it is this cyclist has been dealt with in an entirely routine manner.