Why didn't the Particular Baptists write systematic theologies? Why don't modern Reformed Baptists write them? Why the lack of commentaries, especially historical-theological ones, on the Confession of Faith? These questions have been asked often. Here are some general answers.

Such work requires resources: time and money. You have to have the time to do it, and the time you spend on it has to provide for your family. Consider the output of the the Reformed of the 16th-century, and early 17th, centuries, in the context of a magisterial reformation.

They were writing in large institutions, often universities. The government, and society, held up these institutions. And the institutions, in turn, provided a context where dedicated academic work was given time and money. Their output was incredible. A true treasure trove.

Even for c16 & c17 theologians who were ministers, not professors, they were often in state-churches, whose income was guaranteed by tithe (i.e. tax) at least to a certain level. They are, in a sense, just doing their job. The system promotes and supports that work.

The early English Baptists had none of these advantages, and many disadvantages. They were almost always bi-vocational by necessity. If they had common agreement with much of Ref Theology (cf. 1LCF & 2LCF), there was little time, no money, and few reasons to exert the effort.

In more modern times, Reformed Baptist churches are small and their associational unity has been very badly fractured. We might say that rarely have Reformed Baptists united sufficiently to establish and maintain the superstructure necessary for high-quality dedicated study.

Until Reformed Baptists can unite to contribute resources to a common cause that would empower and enable their own scholars to do the work they desire, they won't see much apart from the dedicated willingness of unpaid labor given in fleeting spare time. Solutions?

1. The superstructure must be built from the ground up. A sorority of churches and fraternity of ministers can only grow from investment in local associations. These could cooperate for common causes. Baptist associations have failed for many reasons. Few want to talk about this.

2. You can bypass the superstructure with a select source of financial support. It's 2020. Crowdsourcing can fund individual scholars, similar to books published "by subscription" in the 18th & 19th century. "I want to write this book, will you pre-fund me, and receive a copy?"

3. Bypass the crowdsourcing and get a true patron who says, "I'll provide the means. You do the work." Few persons with the necessary wealth would invest in a project that won't break even. Even if their estimation of value is more than $, is it wise stewardship on their part?

4. Churches blessed with wealth could fund resident scholars, perhaps. But this often leads to idiosyncrasy. There is no academic environment, no "hear me out" or "what do you think" or "what have you been working on?" Some of the previous suggestions are vulnerable to this, too.

TLDR: 1689rs have not produced and do not produce much in the way of high-quality resources because they do not unite sufficiently to generate the contextual structure necessary for such work.