Every input (shown on the left) needs ~148 (or 180[1]) bytes and this TX has 290 inputs. 290*180 = 52 200 ~= 52 135.
It may be useful to put the full 'calculation' for the TX size in here (unless something has changed):
in*180 + out*34 + 10 plus or minus 'in'
https://bitcoin.stackexchange.com/questions/1195/how-to-calculate-transaction-size-before-sending
Generally I recommend that people combine outputs whenever they can. This is also beneficial for the network as it reduces the UTXO set.