" My guess is EPD did that to have enough money to buy Martin."
My guess is different than yours. MMLP is controlled by MRMC and Alinda. If EPD bought Martin, they'd have to buy MRMC and take out Alinda. Plus, MMLP doesn't really have any compelling assets left, my opinion, that strategically fit for EPD. What's left is mostly 'rounding error' stuff to EPD; MMLP does have access to deepwater at Beaumont which might be interesting.
My guess would be that EPD is upsizing its revolver because a) risk of cash flows being delayed or reduced if any producers file Ch 11, b) easy access to cash in case any specific assets become available (including an asset or two from MMLP, although I doubt that as noted above), which allows them to close quickly without financing contingencies.