In what way, unless they issued shares on the basis of "you buy these, we'll improve the stadium" I don't think they have any kind of obligation
Failure to invest devalues their asset, in turn has long term impact on shareholder value, this is their obligation to maintain and grow shareholder value.
The point was not limited to the facilities, they need the club to remain successful to keep revenues consistent from commercial deals. At this point without significant investment in squad and facilities that is at risk. Partly because rivals have taken levels of investment to new heights, and the club has underinvested in its facilities (assets which have book value, and provide revenue outside of matchdays e.g hosting NFL, concerts etc). This is coupled with sharp rise in borrowing costs against an asset that is already well leveraged.
Anyway its being reported now that full sale before summer is the most likely outcome (no surprise there)
They need to invest or risk devaluing clubs book value long term. They cannot leverage the club any further to fund said investment. Investors smell desperation (on the ropes)