The main thing to keep in mind when reading the inevitable replies to this thread, is that as soon as you ask for an opinion on someone else's motives, you're asking for speculation and not fact.
It's also important to remember that, despite what people here generally claim, there is no single dev team "in charge", "in control" or "in authority". That runs wholly contrary to the values of open source and permissionlessness which Bitcoin was founded upon.
Personally, I prefer to believe the differences are ideological and (for the most part) not malicious, but at the same time, I'm pretty sure I'm in the minority on that one and fighting against the tide of the general forum narrative. Make of that what you will. In essence, it boils down to two distinct views. Those who want to prioritise keeping the blocksize as small as possible to guarantee decentralisation of non-mining nodes of the network, even if it is at the expense of throughput and users being able to transact cheaply and efficiently. Then there are those who feel that there is room to manoeuvre on the blocksize if it helps guarantee users being able to transact cheaply and efficiently. Equally those who would prioritise what tend to be referred to as "off-chain transactions" over "on-chain transactions" and opinions are equally divisive there too. I try to keep myself somewhere in the middle, believing that both arguments have merit. Can't help you with a timeline, although I'm sure I remember people maintaining such a thing somewhere.
//EDIT: Google found this:
http://btcnews.jp/wp-content/uploads/2017/06/blocksize_debate_timeline_en.pngNot sure if that's what you had in mind or not, but hope it helps.
