Although Jordan Graham is clearly a class above, he also has a pretty horrendous injury record, which was the reason we got him on loan the first time. He has even missed a few games this season.
By my calculation, he has managed 65 senior appearances in senior football over 7-8 seasons:
Jordan Graham - Wikipedia
There would therefore be a risk in offering him an extra long contract, and a risk for anyone trying to take him off us.
Dom Samuel has also had long injury issues which was why we were able to get him on a free, and will be paying him for inaction for most of the rest of the season.