At the time, JPMorgan had around 4500 Python devs globally and many of the FX/Commodities/Credit/Rates trading systems were Python-based (Google for Athena or watch [2]).
I felt the bank had gained hugely from the Python community so it was only appropriate to give something back. Fortunately I had lots of support from my MD internally. Ultimately the budgets were controlled from New York and it took time for the approval discussion between London and New York to conclude.
We took sponsorship packages that included logo on banners, an intro during the opening keynote, a recruiting booth, and entry passes for 10 of our devs. The money paid to PyConUK was small in corporate terms, and certainly less than the cost of the time I and the recruiting lead invested in getting it going.
The net result was a good amount of exposure, lots of people saying "I didn't know JPMorgan used Python", two direct hires I think, and useful support for Python in the UK.
I'm no longer at JPMorgan but as long as my future employers benefit from my Python experience, I'll look for ways for them to give back to the community. If you are in the same position, please encourage your employer to do it too. (I'm happy to be quoted on the benefits; my email is in my profile here).
[1] https://pyvideo.org/pycon-uk-2017/pycon-uk-2017-jp-morgan-sp...
[2] https://pyvideo.org/pydata-london-2018/python-at-massive-sca...