Block size debate history lesson - a history of declining BTC marketshare
I have an
alternative view point.
Why don't your correspond your graph to the problem with
Unconfirmed Transactions and increased Delays and Increased Fees.
Those are the real culprits , IMO.
No one would give a crap about blocksize if BTC was handling the transaction load, which it is not!
Ergo the transaction limit and Fee increases are the real cause of the declining market share. 
FYI:
BTC officially sucks, $ .60 fee to send BTC, this is on top of a $2 cost to convert from FIAT to BTC.
So now the Minimum Cost to send $20 of BTC is $2.60 .
That is a 13% fee of the total amount.It is now cheaper to send money by using a Money Order than BTC, and with the large # of unconfirmed transactions,
mailing a money order may be faster.BTC is Now Slower than the US Postal Service, 